Single wall carbon nanotube double quantum dot

We report on two top-gate defined, coupled quantum dots in a semiconducting single wall carbon nanotube, constituting a tunable double quantum dot system. The single wall carbon nanotubes are contacted by titanium electrodes, and gated by three narrow top-gate electrodes as well as a back-gate. We show that a bias spectroscopy plot on just one of the two quantum dots can be used to extract the addition energy of both quantum dots. Furthermore, honeycomb charge stability diagrams are analyzed by an electrostatic capacitor model that includes cross capacitances, and we extract the coupling energy of the double quantum dot.Comment: Published in Applied Physics Letters 4 December 2006. http://link.aip.org/link/?APL/89/23211

The mission oriented terminal area simulation facility

The Mission Oriented Terminal Area Simulation (MOTAS) was developed to provide an ATC environment in which flight management and flight operations research studies can be conducted with a high degree of realism. This facility provides a flexible and comprehensive simulation of the airborne, ground-based and communication aspects of the airport terminal area environment. Major elements of the simulation are: an airport terminal area environment model, two air traffic controller stations, several aircraft models and simulator cockpits, four pseudo pilot stations, and a realistic air-ground communications network. MOTAS has been used for one study with the DC-9 simulator and a series of data link studies are planned in the near future

Preterm labour - Is Mycoplasma hominis involved?

Objective. To assess whether Mycoplasma hominis is associated with preterm labour in primigravidae  and multigravidae with previous midtrimester abortion or preterm labour.Design. Cohort analytical study. Setting. Tygerberg Hospital, a tertiary academic hospital in the Western Cape.Methods. Gram's stains were done on smears taken from the posterior vaginal fornix, at the first  antenatal visit, between 16 and 26 weeks' gestation, in primigravidae and multigravidae at risk for preterm labour. Cultures for M. hominis and other commonly occurring organisms were done ·from endocervical swabs taken at the same visit. The outcome of pregnancy in mothers with positive cultures for M. hominis was then compared with outcome in women with negative cultures.Outcome measures. Prevalence of Chlamydia trachomatis, Ureaplasma urealyticum, bacterial vaginosis and preterm delivery, birth weight and perinatal deaths.Results. Cultures for M. hominis were positive in 83 patients  (21 %) and negative in 312 (79%).  Significantly more mothers in the positive group (40%) delivered before 37 weeks' gestation than in the negative group (28%, P = 0.0313). Their babies weighed significantly less (2 669 g v. 2 864 g, P = 0.0141). The positive group was also associated with more alcohol use in pregnancy and fewer of them  were married. C. trachomatis was found in 18% of mothers in the positive group but in 8% of the negative group (P = 0.0082). U. urealyticum was cultured in 96% of mothers in the positive group in contrast to 81 % in the negative group (P = 0.001). Bacterial vaginosis was observed on 75% of mothers  with positive cultures for M. hominis but in 22% with negative cultures (P = 0.00001, odds ratio 10.21, 95% confidence interval: 5.63 - 18.65). Conclusion. Positive culture for M. hominis was associated with more preterm deliveries and also with a higher frequency of C. trachomatis, U. urealyticum and bacterial vaginosis

Identification of Soil-Water Chemical Parameters for the Prediction and Treatment of Suspended Solids in Surface Water Reservoirs of Coal Mine Lands

High concentrations of suspended solids in coal mine sedimentation ponds are a factor in lowering water quality. This study focuses on the influence dissolved solids have on concentration and settling of suspended solids. Water samples from sedimentation ponds in Eastern and Western Kentucky were used to evaluate water composition in such ponds. Spoil samples from surface mine sites in both parts of the state were used to evaluate water composition released from the spoils upon introducing water. The results demonstrate that water quality emanating from coal spoils of Eastern and Western coal mines is dependent on the type of spoil and/or geologic strata represented. Water composition of randomly selected sedimentation ponds revealed that the relationship between electrical conductance (EC) in mmhos cm-1 and ionic strength (I) of water is I = 0.012 [EC]. Furthermore, it was determined that there is a linear relationship between the repulsive index, RI = [(0.012)(EC)]-1/2 (based somewhat loosely on double-layer theory), and suspended solids. Kinetic data on settling of suspended solids has shown that upon increasing the ionic strength of the water (consequently decreasing RI), the rate of settling increased dramatically. The critical RI at which complete removal of all suspended solids, estimated by graphic extrapolation, is shown to be dependent on the percent base saturation. The data also demonstrate that the critical RI (RI at maximum flocculation) varies depending on the spoils mineralogical and chemical composition. The overall study shows that decreases in suspended solids in coal mine sedimentation ponds can be brought about by relatively small increases in ionic strength. Several approaches as to how one might increase water ionic strength in sediment ponds are discussed

Identification of Soil-Water Chemical Parameters for the Prediction and Treatment of Suspended Solids in Surface Water Reservoirs of Coal Mine Lands

High concentrations of suspended solids in coal mine sedimentation ponds are a factor in lowering water quality. Colloidal particle settling simulations were carried out in the laboratory to test the influence pH and dissolved solids have on concentration and settling rates of suspended solids. The results of the study reveal that the pH range of colloidal coflocculation for the samples tested is between 3.5 and 4.5. Furthermore, liming simulation of acidic sediments, as expected increased colloid dispersion. This increase was dependent on the magnitude of the sodium adsorption ratio (SAR). The greater SAR systems maintained a greater concentration of colloidal suspended particles. However, for the same SAR value when the ionic strength was increased from 4 meq L-1 to 8 meq L-1, sedimentation rate of colloidal particles decreased. The data also show evidence that for the same SAR values when substituting magnesium for calcium, the rate of particle settling increased for one sample but decreased for another. This unexpected behavior is under further investigation

Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots

By means of sequential and cotunneling spectroscopy, we study the tunnel couplings between metallic leads and individual levels in a carbon nanotube quantum dot. The levels are ordered in shells consisting of two doublets with strong- and weak-tunnel couplings, leading to gate-dependent level renormalization. By comparison to a one- and two-shell model, this is shown to be a consequence of disorder-induced valley mixing in the nanotube. Moreover, a parallel magnetic field is shown to reduce this mixing and thus suppress the effects of tunnel renormalization.Comment: 5 pages, 3 figures; revised version as publishe

Preterm labour - is bacterial vaginosis involved?

Objective. To assess the efficacy of treatment of bacterial vaginosis (BV) using metronidazole to reduce  preterm labour in primiravidae and multigravidae with previous midtrimester abortion or preterm labour.Design. Randomised controlled trial.Setting. Tertiary academic hospital.Method. Two different groups of patients were screened for BV at the first antenatal visit, namely  primigravidae and high-risk multigravidae who had had a previous midtrimester abortion or preterm delivery. Patients where BV was diagnosed clinically or on Gram's stain of a smear taken from the posterior vaginal fornix, received either 400 mg metronidazole, or 100 mg vitamin C orally twice daily for 2 days. The Gram's stain was repeated after 4 weeks. If BV W?S found again, treatment with the same  drug was repeated.Outcome measures. Preterm delivery, birth weight and perinatal deaths.Results. One thousand and five patients entered the study, but 40 were excluded for various reasons and 10 were lost to follow-up. There were 464 primigravidae, of whom 150 (32%) had BV. Except for the 5-minute Apgar score, no significant differences were found between primigravidae negative for BV and those who received either metronidazole or vitamin C. There were 491 high-risk multigravidae, of whom 127 (26%) had BV. The mean gestational age in the BVnegative group was 37 weeks, in contrast to 37.4 weeks in the vitamin C group and 35.6 weeks in the metronidazole group. Birth weights in these three groups were 2 752 g, 2 759 g and 2 475 g respectively, significantly less (P == 0.0109) in the  metronidazole group in comparison with the BV-negative group. Delivery before 37 weeks occurred in 29% of high-risk multigravidae with no BV but in 24% of those who took  vitamin C and in 43% who took metronidazole. Differences were significant between the BV-negative and metronidazole groups (P = 0.0231) and also between the metrol'.idazole and vitamin C groups (P = 0.0274). Delivery before 28 weeks occurred in 4% of the high-risk multigravidae with no UV but in 10% of those with BV who took metronidazole. The difference was significant (P =0.0430). Analysis for maximum likelihood estimates for preterm labour identified only previous preterm labour or midtrimester abortion as risk factors.Conclusion. Metronidazole does not seem to reduce the prevalence of preterm labour when given for BV before 26 weeks' gestation

Superconductivity-enhanced bias spectroscopy in carbon nanotube quantum dots

We study low-temperature transport through carbon nanotube quantum dots in the Coulomb blockade regime coupled to niobium-based superconducting leads. We observe pronounced conductance peaks at finite source-drain bias, which we ascribe to elastic and inelastic cotunneling processes enhanced by the coherence peaks in the density of states of the superconducting leads. The inelastic cotunneling lines display a marked dependence on the applied gate voltage which we relate to different tunneling-renormalizations of the two subbands in the nanotube. Finally, we discuss the origin of an especially pronounced sub-gap structure observed in every fourth Coulomb diamond

Initial results from the Caltech/DRSI balloon-borne isotope experiment

The Caltech/DSRI balloonborne High Energy Isotope Spectrometer Telescope (HEIST) was flown successfully from Palestine, Texas on 14 May, 1984. The experiment was designed to measure cosmic ray isotopic abundances from neon through iron, with incident particle energies from approx. 1.5 to 2.2 GeV/nucleon depending on the element. During approximately 38 hours at float altitude, 100,000 events were recorded with Z or = 6 and incident energies approx. 1.5 GeV/nucleon. We present results from the ongoing data analysis associated with both the preflight Bevalac calibration and the flight data

Observation of polarization quantum noise of laser radiation in Rb vapor cell

We present experimental study of polarization quantum noise of laser radiation passed through optically think vapor of Rb87. We observe a step-like noise spectrum. We discuss various factor which may result in such noise spectrum and prevent observation of squeezing of quantum fluctuations predicted in Matsko et al. PRA 63, 043814 (2001).Comment: 4 pages, 5 figures. Translated from Russian by I. Novikov