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International audience; Essential oils (EO) of nutmeg (Myristica fragan Houtt) have a different chemical composition according to their origin. So it is important that laboratories of quality control have a fast and effective method of analysis to prevent frauds and adulteration. The analytical method generally employed [1], is time consuming and two pairs of compounds were not resolved (sabinene/β-pinene, p-cimene/limonene). In order to optimize the GC separation, while reducing the analysis time, we have identified the influential analytical factors among 11 by using a screening of factors: 5 factors are influent. After, we studied the interactions between these 5 factors by using a fractional factorial experiment matrix 2 5 – 1 in 16 experiments [2] and by considering the interactions effect of first order b ij. This optimization allowed to reduce analysis time (20 min instead of 55 min) and to improve the separation between the unresolved compounds (Resolution > 1.5). This method was applied to differentiate EO from ripe nutmeg and those from maces: a chemometric treatment (PCA) of GC data was carried out. The repartition of samples in a 3D score plot (PC1; PC2; PC4 explained variance 81%) show two groups: the maces and the ripe nutmeg. The study of loading associated to these compounds showed that the EO of maces are different on the basis of their content of phenylpropenic compounds (eugenol, myristicin, safrol...) while the EO of ripe nutmegs is characterized by the content of terpenic compounds (α and γ-terpinene, sabinene, α and β-pinene...). However, an overlap of the different classes exists. So the supervised classification method SIMCA [3] was used. Four samples of each origin were used to build the disjoint PCA and three from the same origin to test the models: all the samples are well classified. This study allowed to reduce analysis time and to improve the separation between all the compounds, and to differentiate EO from their origin: this method can be used as quality control.

International audience; Gamma radiolysis was investigated on a nuclear grade mixed bed ion exchange resin and its pure components under different irradiation conditions. Screening designs were performed to identify the factors influencing gas production after their γ-radiolysis and to compare their γ-degradation stability. Only hydrogen and trimethylamine quantities were considered as the response in the experimental designs. The other detected gases and water-soluble products were used to improve the resins degradation. Aerobic irradiation atmosphere decreased the H 2g production of AmbOH, MB400, and amines. The water presence increased the H 2g quantities for AmbH and decreased those for MB400 resin. Liquid water had no effect on H 2g production from AmbOH but was favorable to increased amine production. The H 2g production of AmbH increased with the absorbed dose that had little effect on the AmbOH resin. No impact of dose on the H 2g production was detected for MB400 that appeared to be less degraded.

Some spiro[indoline-naphthoxazines] I and spiro[indoline-pyridobenzoxazines] II substituted by different groups were synthesized in order to evaluate their photochromic properties1 and to optimize the preparation of spiroheterocyclic systems. In addition, some spiro[indoline-naphthopyrans] III were also prepared as reference compounds. Their physical and spectroscopic characteristics (UV, 1H and 13C NMR) were determined. A study using the experimental design methodology allowed to point out the most important factors for improving the reaction yields.

High mobility two-dimensional electron systems in GaN/AlGaN heterostructures have been realized by plasma assisted molecular beam epitaxy on GaN templates. In the density range of 10 11 cm -2 to 10 12 cm -2 , mobility values exceeding 160000 cm 2 /Vs have been achieved. Scattering mechanisms that presently limit the production of higher mobility samples are discussed. We present results of a systematic study of the weak localization and antilocalization corrections to the classical conductivity at very low magnetic fields. The unambiguous observation of a conductivity maximum at B = 0 suggests that spin-orbit scattering is not negligible in GaN heterostructures as one might expect for a wide-bandgap system. We have recently realized electron transport through GaN nanostructures. We report on the transport properties of the first quantum point contacts (QPCs) in GaN. These devices are used to study one-dimensional transport in the Nitride system.

We demonstrate GaAs-based, metal-oxide-semiconductor field-effect transistors (MOSFETs) with excellent performance using an Al2O3 gate dielectric, deposited by atomic layer deposition (ALD). This achievement is very significant because Al2O3 possesses highly desirable physical and electrical properties as a gate dielectric. These MOSFET devices exhibit extremely low gate-leakage current, high transconductance, and high dielectric breakdown strength. A short-circuit, current-gain, cutoff frequency (fT) of 14 GHz and a maximum oscillation frequency (fmax) of 25.2 GHz have been achieved from a 0.65-µm gate-length device. The interface trap density (Dit) of Al2O3/GaAs is evaluated by the hysteresis of drain-source current, Ids, versus gate-source bias, Vgs, and the frequency dispersion of transconductance, gm.

Employing Ga 2 O 3 (Gd 2 O 3 ) as gate dielectric and Si-doped GaAs as conducting channel, depletion-mode GaAs MOSFETs were fabricated. DC I – V and transfer curves show no pinch-off and drain current hysteresis. Etching a thin layer from the top of Ga 2 O 3 (Gd 2 O 3 ) in the gate region before gate metal deposition leads to full pinch-off and significantly reduces the drain current hysteresis. This process may remove the contaminated Ga 2 O 3 (Gd 2 O 3 ) due to exposure to chemicals and prior processes, and thus results in a clean gate metal to oxide interface. The clean gate metal to Ga 2 O 3 (Gd 2 O 3 ) interface also leads to higher DC transconductance, higher unity current gain cut-off frequency as well as higher unity power gain cut-off frequency as compared with GaAs MOSFET devices with a contaminated metal/oxide interface at the gate.

Our ability of controlling the growth and interfaces of thin dielectric films on III–V semiconductors by ultrahigh vacuum deposition has led to investigations of gate stacks containing rare earth oxides of Gd 2 O 3 and Y 2 O 3 as alternative high κ gate dielectrics for Si. The abrupt interfaces achieved in these gate stacks have enabled the electrical, chemical, and structural studies to elucidate the critical materials integration issues for CMOS scaling, including morphology dependence, interfacial structure and reaction, thermal stability and gate electrode compatibility.

We report on an extensive study of the growth and transport properties of the two-dimensional electron gas (2DEG) confined at the interface of AlGaN/GaN heterostructures grown by molecular beam epitaxy (MBE) on thick, semi-insulating GaN templates prepared by hydride vapor phase epitaxy (HVPE). Thick (∼20μm) GaN templates are characterized by low threading dislocation densities (∼5×10 ⁸cm ⁻²) and by room temperature resistivities of ∼10 ⁸cm. We describe sources of parasitic conduction in our structures and how they have been minimized. The growth of low Al containing (x≤0.05) Al ₓGa ₁₋ₓN/GaN heterostructures is investigated. The use of low Al containing heterostructures facilitates the study of the 2DEG transport properties in the previously unexplored regime of carrier density n s≤2×10 ¹²cm ⁻². We detail the impact of MBE growth conditions on low temperature mobility. Using an undoped HVPE template that was residually n type at room temperature and characterized an unusually low dislocation density of ∼2×10 ⁸cm ⁻², we have grown an Al ₀.₀₅Ga ₀.₉₅N/GaN heterostructure with a record mobility of 75000cm ²/Vs at sheet density of 1.5×10 ¹²cm ⁻² and T=4.2K. The same heterostructure design grown on a semi-insulating HVPE template yielded a peak mobility of 62000cm ²/Vs at a density of n s=1.7×10 ¹²cm ⁻² and T=4.2K. The observation of the fractional quantum Hall effect at filling factor ν=5/3 in the AlGaN/GaN system is reported. It is also demonstrated that thick semi-insulating GaN templates grown by HVPE are a viable substrate for the growth of high electron mobility transistors. Typical Al ₀.₂₅Ga ₀.₇₅N/GaN heterostructures exhibit room temperature density of 1.0×10 ¹³cm ⁻³ and mobility of ∼1500cm ²/Vs. The dc and rf characteristics of transistors grown by MBE on a HVPE template are presented. © 2002 American Institute of Physics.

Using several derivatives of scanning force microscopy with conducting tips, we find direct evidence for the existence of a highly compensated donor impurity band in GaN films near the sapphire substrate interface. Scanning current-voltage and capacitance microscopy measurements both show that the free electron density is much higher in the interfacial region of these films. However, surface contact potential images reveal that the Fermi level in the interfacial region is 50 meV to 100 meV deeper into the bandgap than it is in the less conducting bulk film. These results are inconsistent with a high density of electrons in the intrinsic conduction band. Rather, they point to the existence of a partially filled donor impurity band with the Fermi level in the impurity band. We show that this anomalous conduction behavior most likely originates from a high concentration of oxygen and the defective microstructure at the GaN/sapphire interface.

Thermal degradation of polystyrene and polyvinylchloride was studied by thermomanometric analysis. A design of experiments was used to quantify the influence of 8 physico-chemical parameters on the responses of the analyser and on the different types of degradation compounds.

The study of the thermal degradation of the fireproof polystyrene—butadiene copolymer by an intumescent system: ammonium polyphosphate (APP)—pentaerythritol (PER)—talc (TAL), was done through an experimental process. Thermogravimetry under air sweeping was used. We observed for the degradation rate of the mixture with fireproofing agents, in the field of 20 to 50% mass loss, a better linear increasing when this mixture contains more TAL and the ratio APP/PER is smaller.

The oxytribromide Ag0.37WOBr3 crystallizes in the triclinic system: a = 3.766(3), b = 7.101(7), c = 10.49(1) A, α = 101.80(5)°, β = 100.25(5)°, γ = 105.34(5)°, with the space group P 1 . The crystal structure determined from single crystal X-ray diffraction data is based on W2Br6 units, with short W-W distances, joined by W-O-W bonds to form [W2Br6O4/2]1∞ infinite chains developing along the a direction. Along the c direction, the cohesion between the chains is achieved by silver atoms which exhibit statistical distribution; along the b direction exist only van der Waals Br-Br contacts between adjacent chains. These weak linkages between the chains in two directions of the space give a strong one-dimensional character to this new tungsten oxybromide.

The aim of this study was to prepare, in a reproducible manner, poly( d , l -lactide-co-glycolide) (PLGA) biodegradable microparticles with high encapsulation yield of nerve growth factor (NGF), a neurotrophic factor of interest in the treatment of neurodegenerative diseases. Human serum albumin (HSA) was co-encapsulated with NGF by the w/o/w emulsion solvent evaporation/extraction method to stabilize the primary emulsion and to protect NGF. The encapsulation yield optimization was first carried out with HSA alone since it was the major component in the final microspheres, as compared to NGF. The effects of ten process factors on HSA entrapment in PLGA microspheres were examined using a fractional factorial design. Four major factors were identified. The presence of carboxymethylcellulose sodium or mannitol in the internal aqueous phase, the increase of the internal aqueous volume and the concentration of HSA led to a decrease of the encapsulation yield. Two main factors, namely the internal aqueous phase volume and the proportion of acetone in the organic phase, previously identified as a predominant factor, were studied through a response surface methodology. The observed range of HSA encapsulation yield was 87.4–100%. NGF was encapsulated according to the optimal conditions found for the entrapment of HSA. The encapsulation yield was then 97.3±5.0%.

International audience; During cleaning steps, ultrafiltration membranes are mechanically and chemically stressed. This may result in membrane degradations and failures. In this paper, polysulfone membranes were used to evaluate membrane deteriorations by commercial detergents in static conditions. Ageing of the membrane was simulated by immersing samples in solutions containing commercial detergents with various concentrations, temperatures and times defined by experimental designs. Indeed, an innovative approach in the chemical membranes ageing researches, based on methodological tools, was used in order to achieve significant ageing experiments without using an accelerated ageing protocol. The macroscopic changes were monitored by permeability measurements and mechanical strength tests coupled with a microscopic characterization by ATR-FTIR and HRSEM. The present work details results obtained for three commercial detergents: an alkaline, an acidic and an enzymatic detergent. It was found that the detergents used in the industrial advised conditions (concentration, temperature and time of contact) were not detrimental for membrane properties (permeability and elongation at break) and so for the quality of the produced water. Over the industrial cumulated time of contact, different ageing effects can be observed and compared with the ones induced by NaOCl.

International audience; During cleaning steps, ultrafiltration membranes are mechanically and chemically stressed. This can result in membrane degradations, failures, and be shut down for membrane replacement and therefore affect the production rate of the process and its sustainability. These phenomena raise the problem of necessary optimization of the cleaning procedures that have to tackle simultaneously, the best cleaning efficiency and the less detrimental procedures for the membranes. Despite the fact that aging is becoming a major issue between end-users, membrane manufacturers, and chemical product suppliers, there is considerably less literature dedicated to membrane aging than to cleaning. First, this study briefly reviews articles dedicated to aging damages involved by NaOCl and commercial detergents (especially on polysulfone ultrafiltration membrane). Then, the present study details the innovative way setup: "Designs of experiments" is used to provide additional data that help with a thorough understanding of membrane aging. Thus, contrary to the accelerated aging approach that is commonly used in membrane-aging researches (concentration per time of contact: "c × t parameter"), designs of experiments were used to organize at best the aging experiments in order to achieve a relevant establishment of an aging pattern. Results show that this scientific approach provides a satisfying and reliable pattern to simulate membrane aging in function of the chosen chemical parameters.

For the first time, a III-V compound semiconductor MOSFET with the gate dielectric grown by atomic layer deposition (ALD) is demonstrated. The novel application of the ALD process on III-V compound semiconductors affords tremendous functionality and opportunity by enabling the formation of high-quality gate oxides and passivation layers on III-V compound semiconductor devices. A 0.65-/spl mu/m gate-length depletion-mode n-channel GaAs MOSFET with an Al/sub 2/O/sub 3/ gate oxide thickness of 160 /spl Aring/ shows a gate leakage current density less than 10/sup -4/ A/cm/sup 2/ and a maximum transconductance of 130 mS/mm, with negligible drain current drift and hysteresis. A short-circuit current-gain cut-off frequency f/sub T/ of 14.0 GHz and a maximum oscillation frequency f/sub max/ of 25.2 GHz have been achieved from a 0.65-/spl mu/m gate-length device.

We demonstrate a dual wavelength mid-infrared Quantum Cascade Laser (QCL) utilizing a single active region to emit at 5-μm and 9-μm. The novelty lies in the large energy difference between the two lasing energies, achieved through simultaneous injection into the top 2 levels of a 4-level cascade employing InGaAs/InAlAs heterostructures latticematched to InP. The gain and losses at both wavelengths were measured by two different methods, Hakki-Paoli and cutback method, and were compared with theoretical predictions. The results for the gain of the 9-μm laser from the two techniques are consistently lower than theoretical predictions. Moreover, the mid-infrared losses are larger than expected at both wavelengths. We are investigating these devices for their potential application of quantum coherence to achieve lasing without inversion. The intense fields generated by the 9-μm laser are expected to partially eliminate the resonant absorption on the transition of interest at an energy corresponding to the difference between the energies of the two lasers. Our results on the dual wavelength QCL provide insights in the detail charge transport and optical properties of this design concept and open up the possibility for future optimization of inversionless lasers.

International audience; The development of new technologies for water recycling is a priority for arid and semi-arid countries such as those of the Mediterranean basin. The aim of this study was to test the efficiency of UV-A and UV-C light emitting diodes (UV-LEDs) on bacteria inactivation. We used Escherichia coli and Enterococcus faecalis, bioin-dicators of fecal pollution typically found in urban wastewaters. An experimental design was performed to discriminate weight of factors influencing bacteria inactivation yields and reactivation phenomena. Four parameters were tested on simple bacterial cultures: pH, bacterial density, exposure time and wavelength. It appears that the exposure time and wavelength used have a significant effect on the response. The 280/ 365 nm or 280/405 nm coupled wavelengths, have the most important bactericidal effect, and we also note the absence of bacterial reactivation after 60 s of exposure to UV.

An alternative for the GC determination of permanent gases in Titan's atmosphere, given the severe constraints of space instrumentation, is the use of a 100–120-mesh molecular sieve 5A micropacked column. Because of its high efficiency, small pressure drop and short analysis time, such a column is fully compatible with the experimental constraints of the Cassini-Huygens mission. In order to optimize the GC conditions associated with this column, a methodological approach was supported by a Doehlert experimental design. With such optimized conditions, the column provides a rapid separation of the selected products under isothermal conditions, with about 900 theoretical plates per metre at 70°C for most of the solutes studied.

Synchrotron and Guinier x‐ray powder diffraction data as a function of temperature on a superconducting PbMo6S8 sample (Tc=14.7 K) showed evidence for a subtle structural phase transition at Tl=140 K, leading from a rhombohedral high‐temperature to a triclinic low‐temperature modification. The transition is incomplete and presents a hysteresis of about 110 K. The triclinic cell parameters obtained at 130 K, a=6.534(9) A, b=6.532(9) A, c=6.529(9) A, α=89.27(8)°, β=89.12(8)°, γ=88.97(8)°, show that the distortion affects mainly the angles (δα/αr=0.3%) and less the edges (δa/ar

Scanning Kelvin force microscopy is applied to study the charge nature of threading dislocations on GaN surfaces. On the oxidized surface, the surface potential maps show little change near dislocations, indicating that if the dislocations are charged in the bulk, the charges are either screened or depleted due to band bending. After cleaning in hot H3PO4, the potential near dislocations located at domain boundaries and inside domains is found to be lower, consistent with excess local negative fixed charges. Curiously, no contrast was seen for the screw dislocations at the centers of growth spirals even after H3PO4 treatment. Thus, either these screw dislocations have no gap states, or if they do have gap states, the positions are higher in energy (closer to conduction band edge) than the gap states of other dislocations.

Conditions of microencapsulation by in situ polycondensation, using melamine-formaldehyde as wall material, are influenced by the chemical nature of the core to encapsulate. In our study concerning the encapsulation of a photopolymerizable phase containing an electrically charged compound, it was necessary to modify the experimental process to obtain capsules of good quality. We used the factorial design method of screening by utilization of an asymmetric matrix, according to the collapsing principle of Addleman. The advantage of this method is that it allows determination of the simultaneous influences of the 11 experimental parameters involved in this preparation. The calculation method can be applied to more than two levels for some of the factors. The continuously varying parameters were altered between two extreme levels, chosen to allow encapsulation. For discontinuous factors, such as the molecular weight of the modifying system or nature of the aminoplast, we used the commercially available compounds, respectively three and four kinds. The results of the obtained capsules were determined by comparing microphotographic pictures. With 16 experiments we found four more factors influencing quality of capsules. We also determined the most favourable levels for the other seven parameters. The results allowed us to find optimal conditions in the experimental field. We obtained capsules of a satisfactory quality for this purpose, using only minimum experimentation.

The reverse bias leakage current in macroscopic GaN Schottky diodes is found to be insensitive to barrier height. Using a scanning current–voltage microscope, we show that the reverse bias current occurs at small isolated regions, while most of the sample is insulating. By comparing the current maps to topographic images and transmission electron microscopy results, we conclude that reverse bias leakage occurs primarily at dislocations with a screw component. Furthermore, for a fixed dislocation density, the V/III ratio during the molecular beam epitaxial growth strongly affects reverse leakage, indicating complex dislocation electrical behavior that is sensitive to the local structural and/or chemical changes.

Transcatheter arterial chemoembolization (TACE) offers a survival benefit to patients with intermediate hepatocellular carcinoma (HCC). A widely accepted TACE regimen includes administration of doxorubicin-oil emulsion followed by gelatine sponge-conventional TACE. Recently, a drug-eluting bead (DC Bead ®) has been developed to enhance tumor drug delivery and reduce systemic availability. This randomized trial compares conventional TACE (cTACE) with TACE with DC Bead for the treatment of cirrhotic patients with HCC. Two hundred twelve patients with Child-Pugh A/B cirrhosis and large and/or multinodular, unresectable, N0, M0 HCCs were randomized to receive TACE with DC Bead loaded with doxorubicin or cTACE with doxorubicin. Randomization was stratified according to Child-Pugh status (A/B), performance status (ECOG 0/1), bilobar disease (yes/no), and prior curative treatment (yes/no). The primary endpoint was tumor response (EASL) at 6 months following independent, blinded review of MRI studies. The drug-eluting bead group showed higher rates of complete response, objective response, and disease control compared with the cTACE group (27% vs. 22%, 52% vs. 44%, and 63% vs. 52%, respectively). The hypothesis of superiority was not met (one-sided P = 0.11). However, patients with Child-Pugh B, ECOG 1, bilobar disease, and recurrent disease showed a significant increase in objective response (P = 0.038) compared to cTACE. DC Bead was associated with improved tolerability, with a significant reduction in serious liver toxicity (P < 0.001) and a significantly lower rate of doxorubicin-related side effects (P = 0.0001). TACE with DC Bead and doxorubicin is safe and effective in the treatment of HCC and offers a benefit to patients with more advanced disease. © 2009 Springer Science+Business Media, LLC and the Cardiovascular and Interventional Radiological Society of Europe (CIRSE).

Our objective was to optimize a medium for preadipocyte differentiation into adipocytes. Methods: The differentiation medium contains fixed components as well as 7 variable ones. To perform this study, different experiments were designed and the study was carried out in 4 stages. The first two stages tested the influence of serum, dexam- ethasone, hydrocortisone and an cAMP activator. In the third stage, two new variables were added: rosiglitazone and insulin. In the final stage, the medium selected in stage 3 was validated. The differentiation selection criteria consisted of the number of mature adipocytes and adiponectin secretion. Results: We have shown that each variable was indispensable and that positive interactions occurred between some variables. No negative interactions were found and it was possible to optimize the concentration of each variable. Conclusions: We selected the following medium, which provides optimal adipocyte size and adiponectin secretion: DMEM/HAMF12 + 10% Foetal Clone Serum (FCS) + 2 nM triiodothyronine + 10 nM hydrocortisone + 0.5 mM IsoButyl Methyl Xanthine (IBMX) + 500 nM dexamethasone + 1 µM rosiglitazone + 0.15 UI/ml insulin + antibiotics.

Using several scanning probe techniques to investigate local electronic properties, we show that the GaN/sapphire interfacial region contains ⩾ ten times higher electron density but with the Fermi level being 50–100 meV deeper in the band gap compared to the less-conducting bulk film. This anomalous behavior cannot be explained by transport in the intrinsic conduction band of GaN. Rather, it points to the existence of a partially filled donor impurity band. We relate the presence of this impurity band conduction to excess oxygen in the region and the defective microstructure at the GaN/sapphire interface.

We report on growth and characterization of both epitaxial and amorphous films Gd2O3 of (e=14) and Y2O3(e=18) as the gate dielectrics for Si prepared by ultrahigh vacuum vapor deposition. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single-domain films in the Mn2O3 structure. Typical electrical leakage results are 10−3 A/cm2 at 1 V for single domain epitaxial Gd2O3 and Y2O3 films with an equivalent SiO2 thickness, teq of 15 A, and 10−6 A/cm2 at 1 V for smooth amorphous Y2O3 films (e=18) with a teq of only 10 A. For all the Gd2O3 films, the absence of SiO2 segregation at the interface is established from infrared absorption measurements.

This chapter deals with nonclassical designs needed when classical tools could not be applied, particularly because of various constraints. Several examples of studies related to the development of nonclassical experimental strategies are presented. Mixed studies, which combine discontinuous variables and continuous variables or mixture variables and discontinuous or continuous variables, are considered. Suitable experimental designs that need to be built up in order to take into account particular mathematical models associated to this type of study are discussed.

We present new models which provide satisfactory and low cost modeling of infrared absorption spectra of gases from low to high pressures. The first is a line-by-line approach based on simple and empirical corrections of the lorentzian shape which account for the effects of line-mixing and finite duration of collisions. It leads to satisfactory agreement with experimental infrared spectra in a wide density range. It is degraded for the deduction of a Generalized Narrow-Band Statistical Model (GNBSM) which enables very rapid computation of medium resolution radiative properties. The latter is an extension of the low density (i.e., when lines are much narrower than the considered spectral resolution) approach developed by Goody [1] ; it is based on a random representation of line-positions and statistical description of line integrated-intensities and leads to a very simple expression of spectrally averaged absorption properties of gases. It is consistent with previous low density models and requires computer times several orders of magnitude shorter than line-by-line calculations. Comparisons between degraded approaches, line-by-line models, and experimental results demonstrate the accuracy of the present models in cases where previously proposed approaches are very inaccurate.

We have investigated the stabilization of GexSn1-x on (001) InSb substrates, as well as InSb coated GaAs substrates. We find that alloys up to ≈1500A can be stabilized when 0 0.10, we observe partial phase separation into coherent α-Sn and α-GeSn. The films are stable in the temperature range of 125-130° C, depending on Ge concentration. We present a thermodynamic model which exhibits the trends observed in the growth and stability of epitaxially stabilized GexSn1-x alloys. Electrical and optical measurements show consistently high carrier concentrations (1021 cm-3) and low carrier mobility (

Single crystals of SrxMo6S8 with different strontium concentrations (x 10 K under 20 kbar). The structural transition (Ts) and superconducting critical (Tc) temperatures under pressure for stoichiometric and substoichiometric samples can be described by the same curve, if chemical pressure is taken into account. Comparison is made with EuMo6S8 and related compounds where the cations are magnetic.

N 2 -broadened linewidths have been measured for 27 rotational transitions (from J = 6 to J = 32) in the ground state of hydrogen cyanide. The data were recorded at room temperature using a Fourier transform spectrometer operating in the spectral range 10–100 cm −1 , with an apodized resolution of 0.060 cm −1 . A comparison is made with other experimental data, and with the results obtained from two semiclassical impact theories of collisional broadening.

We present a study of the temperature and density dependence of the resistivity of an extremely high quality two-dimensional hole system grown on the (100) surface of GaAs. For high densities in the metallic regime ($p\agt 4 \times 10^{9}$ cm$^{-2}$), the nonmonotonic temperature dependence ($\sim 50-300$ mK) of the resistivity is consistent with temperature dependent screening of residual impurities. At a fixed temperature of $T$= 50 mK, the conductivity vs. density data indicates an inhomogeneity driven percolation-type transition to an insulating state at a critical density of $3.8\times 10^9$ cm$^{-2}$., Comment: accepted for publication in PRL

Solid-phase extraction (SPE) of trace elements before their analysis has become a conventional pretreatment step of analytes because of their frequent low concentrations in numerous samples. Additionally, interfering compounds often accompagny analytes of interest, thus requiring a clean-up step. The preconcentration step and/or matrix removal can be efficiently improved by chemometric approaches allowing obtention of reliable results. Single variable approach is often used but is time and cost consuming, and may be the source of mistakes; multivariable approach allows to overcome these problems and increases the probability of global optimum finding. In order to obtain a set of experimental conditions for the selective extraction of Al(III) in water samples, onto a modified organic support (salicylic acid grafted on XAD-4), a multicriteria approach (response surface methodology) has been applied. The extraction method was optimized by the aid of a factorial design and a uniform shell Doehlert design for six variables: sample percolation flow rate, trace metal amount, sample volume, concentration and volume of HCl used for elution of aluminium. Results demonstrate the synergic effects of four factors and allow us to define working ranges for each parameter tested. The designed SPE procedure was then sucessfully applied to synthetic and real samples, issued from a potable water treatment unit.

We demonstrate high-reflectivity crack-free Al 0.18 Ga 0.82 N/Al 0.8 Ga 0.2 N distributed Bragg reflectors (DBR) and monolithic microcavities grown by molecular beam epitaxy on thick c-axis GaN templates. The elastic strain energy in the epilayer is minimized by compensating the compressive and tensile stress in every period of the DBR structure. A 25 period DBR mirror provides a 26nm-wide stop band centered at 347 nm with the maximum reflectivity higher than 99%. The high-reflectivity DBRs can be used to form high Q -factor monolithic AlGaN/AlGaN microcavities. INTRODUCTION High-reflectivity distributed Bragg reflect ors (DBR) in the ultraviolet region ar e essential for the development of GaN-based optical devices. In particular, the region around 350 nm is important for devices containing pure GaN as an active medium. The growth of DBRs remains challenging in the nitrid e system. The difficulty lies in maintaining the structural integrity of a relatively thick structure that contains materials with a large lattice constant mismatch and different thermal expansion coefficients. Only a few groups have reported high-reflectivity Al

In this work, Amberlite XAD-4 resin functionalized with salicylic acid was synthetized, characterized and applied as a new packing material for an on-line system to iron determination in aqueous samples. The detection method is based on the sorption of Fe(III) ions in a minicolumn containing the synthesized resin, followed by a desorption step using an acid solution and measurement of iron by vis-spectrophotometry (CAS method). The optimization of the solid-phase extraction system was performed using factorial design and Doehlert matrix considering six variables: sample percolation rate (0.5–9 ml min −1 ), sample metal concentration (20–200 μg l −1 ), flow-through sample volume (0–5 ml) (all three directly linked to the extraction step), elution flow-rate (0.5–9 ml min −1 ), concentration and volume of eluent (HCl 0.1–0.5 M) (all three directly linked to the elution step). The aim of this study was to obtain a set of operating ranges for the six variables tested in order to obtain – by means of a mathematical function allowing maximisation of each response (desirability function) – at least 90% of iron recovery rates. Using the experimental conditions defined in the optimization, the method allowed iron determination with achieved detection limit of 2.3 μg l −1 and precision (assessed as the relative standard deviation) of 9.3–2.8% for iron solutions of 10.0–150 μg l −1 . Real samples (coming from a water treatment unit) were used successfully when evaluating potentialities of the developed SPE procedure coupled to a spectrophotometric determination.

In this paper, a multivariable approach has been applied for the selective removing of Fe(III) and Al(III), in the range 0–200 μg l−1, in water samples onto a modified organic support (salicylic acid grafted on XAD-4). An empirical mathematical model was designed which establishes the relationship between the variation of the responses (extraction yields), and the variation of three factors (sample volume, sample percolation flow rate and amount of metallic ions present in the sample). To estimate the coefficients of the developed model, an uniform shell Doehlert design has been applied; these experiments consisted in GF-AAS determination of aluminium and iron amounts in eluates after percolation of samples through modified support. Results show a similar behaviour of the resin towards aluminium and iron with a preponderant effect of the percolation flow rate value; however this one is crucial for aluminium extraction and should be maintained below to 0.55 ml min−1 to reach a 95% Al3+ extraction yield (versus 2.25 ml min−1 for Fe3+). The optima determined by this experimental design approach have been further applied to the selective extraction of aluminium and iron from multielement synthetic samples and from real samples at the outlet of potable water treatment units.

We present low-temperature magnetoconductivity measurements of a density-tunable and high mobility two-dimensional electron gas confined in the wide band-gap $\mathrm{Ga}\mathrm{N}∕\mathrm{Al}\mathrm{Ga}\mathrm{N}$ system. We observed pronounced antilocalization minima in the low-field conductivity, indicating the presence of strong spin-orbit coupling. Density dependent measurements of magnetoconductivity indicate that the coupling is mainly due to the Bychkov-Rashba mechanism. In addition, we have derived a closed-form expression for the magnetoconductivity, allowing us to extract reliable transport parameters for our devices. The Rashba spin-orbit coupling constant is ${\ensuremath{\alpha}}_{\mathrm{so}}\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\phantom{\rule{0.3em}{0ex}}\mathrm{eV}\phantom{\rule{0.2em}{0ex}}\mathrm{m}$, while the conduction-band spin-orbit splitting energy amounts to ${\ensuremath{\Delta}}_{\mathrm{so}}\ensuremath{\sim}0.3\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ at ${n}_{e}=1\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}$.

The wavelength dependent changes in optical gain and refractive index in a Fabry-Perot semiconductor optical amplifier are measured for various detunings of the pump wavelength from the quasi-Fermi level separation. The refractive index change is nearly constant over a very large wavelength range. We also present data for the linewidth enhancement factor due to optical injection. Estimates of the carrier densities and stimulated recombination rates are made using our optical gain model based on realistic band structure calculations for a strained quantum-well laser. Our results are very useful for ultra-broad-band wavelength conversion by cross-gain and cross-phase modulation (XGM, XPM).

Transmission performance of a 10-Gb/s integrated electroabsorption modulator/DFB laser has been evaluated in terms of the eye margin degradation and the receiver sensitivity penalty caused by the chromatic dispersion in the standard (non-DSF) fiber. Combination of low extinction ratio (/spl epsi/=5 dB) and negative chirp (/spl Delta/v=-0.01 nm) operation allows 10-Gb/s transmission over 130-km standard fiber without any dispersion penalty in receiver sensitivity (for 10/sup -9/ BER) and with a 7% eye margin for 10/sup -15/ BER.

We report on novel tunable three-dimensional solid Fabry-Perot etalons fabricated by the surface-micromachining technique. The Fabry-Perot etalon is monolithically integrated with an on-chip rotation stage for angle tuning. A wavelength tuning range of 45 nm has been achieved at 1.3 /spl mu/m wavelength for a rotation angle of 70/spl deg/. The optical properties of the polysilicon materials have also been characterized using the etalon as testing vehicles.

The aim of this research is to demonstrate the effect of variations in certain parameters of the oily phase (OP) in water-in-oil (W/O) emulsions on rheological and texture properties of finished products. The formulated emulsions were selected according to an optimal experimental procedure. The applied variations were nature of the OP, its volume fraction, the hydrophilic-lipophilic balance (HLB) value, and the surfactant proportion. Results are presented for the followed tests carried out on the emulsions: texture analysis, rheology, and particle size analysis. The oils used in the study were sweet almond oil, liquid paraffin, maize oil, cyclomethicone, dimethicone, and wheat germ oil. The resulting data demonstrate a notable influence of the volume fraction oil on hardness, viscosity, adhesiveness, and cohesiveness of W/O emulsions. Emulsion hardness and viscosity increased as the OP percentage increased; this effect being even more pronounced for the vegetable oils. In contrast, emulsion adhesiveness and cohesiveness decreased as the volume fraction oil increased. The HLB value of the surfactant mixture of the emulsion also influenced hardness, adhesiveness, and elasticity, increasing or decreasing as HLB value did.

In this paper, we demonstrate for the first time GaAs-based MOSFETs with excellent performance using of CVD is a very robust, highly manufacturable process.

Pyrolyser-gas chromatography-mass spectrometry was used to analyze polycyclic aromatic hydrocarbons in contaminated soil without preliminary extraction. Experimental research methodology was used to obtain optimal performance of the system. After determination of the main factors (desorption time, Curie point temperature, carrier gas flow), modeling was done using a Box-Behnken matrix. Study of the response surface led to factor values that optimize the experimental response and achieve better chromatographic results.