250 research outputs found
Charge transfer and Fermi level shift in p-doped single-walled carbon nanotubes
The electronic properties of p-doped single-walled carbon nanotube (SWNT) bulk samples were studied by temperature-dependent resistivity and thermopower, optical reflectivity, and Raman spectroscopy. These all give consistent results for the Fermi level downshift (Delta E(F)) induced by doping. We find Delta E(F) approximate to 0.35 eV and 0.50 eV for concentrated nitric and sulfuric acid doping respectively. With these values, the evolution of Raman spectra can be explained by variations in the resonance condition as E(F) moves down into the valence band. Furthermore, we find no evidence for diameter-selective doping, nor any distinction between doping responses of metallic and semiconducting tubes
Electronic Structure of Carbon Nanotube Ropes
We present a tight binding theory to analyze the motion of electrons between
carbon nanotubes bundled into a carbon nanotube rope. The theory is developed
starting from a description of the propagating Bloch waves on ideal tubes, and
the effects of intertube motion are treated perturbatively in this basis.
Expressions for the interwall tunneling amplitudes between states on
neighboring tubes are derived which show the dependence on chiral angles and
intratube crystal momenta. We find that conservation of crystal momentum along
the tube direction suppresses interwall coherence in a carbon nanorope
containing tubes with random chiralities. Numerical calculations are presented
which indicate that electronic states in a rope are localized in the transverse
direction with a coherence length corresponding to a tube diameter.Comment: 15 pages, 10 eps figure
First Investigation of the Composition and Spatial Distribution of Polychaete Feeding Guilds from Essaouira Protected Coastal area (Atlantic Coast of Morocco)
Several researches have been conducted to explain patterns of the abundance, richness and taxonomic diversity of benthic polychaetes; however, such analyses have ignored the functional diversity of polychaete communities, especially feeding guilds in intertidal rocky shores. The present study was carried out to describe and analyse the polychaete feeding guilds on intertidal rocky shores and then examine the effects of environmental factors. Twelve intertidal rocky shores from the coastal protected
area of Essaouira (Atlantic coast of Morocco) were sampled during the summer of 2016. A total of 42 polychaete species belonging to 29 genera and 16 families were identified among the 4517 specimens collected. The medium biomass per sampling site was found to be 37.61 ± 15.80 g.m-2
. The polychaete species were classified into five feeding guilds, and nine feeding modes. The filter feeders were the
dominant feeding guild (32%) followed by omnivores (23%), burrowers (20%), carnivorous (15%) and surface deposit-feeders (10%). The FDT (filter feeder, discretely motile, with tentacles) was the most abundant feeding mode, accounting for 24% of abundance (mainly represented by Sabellaria alveolata), followed by the ODJ feeding mode (omnivorous, discretely motile, with jaw apparatus) with 22%, and the SDT feeding mode (surface deposit feeder, discretely motile, with tentacles) with 18.9%. The highest
trophic importance index and index of trophic diversity values were recorded in the southern region of Essaouira coastline. Based on the canonical correspondence analysis, composition and spatial distribution of polychaete feeding guilds were mainly related to the length of rocky shores and water temperature
Socioeconomic and geographic determinants of survival of patients with digestive cancer in France
Using a multilevel Cox model, the association between socioeconomic and geographical aggregate variables and survival was investigated in 81 268 patients with digestive tract cancer diagnosed in the years 1980–1997 and registered in 12 registries in the French Network of Cancer Registries. This association differed according to cancer site: it was clear for colon (relative risk (RR)=1.10 (1.04–1.16), 1.10 (1.04–1.16) and 1.14 (1.05–1.23), respectively, for distances to nearest reference cancer care centre between 10 and 30, 30 and 50 and more than 90 km, in comparison with distance of less than 10 km; P-trend=0.003) and rectal cancer (RR=1.09 (1.03–1.15), RR=1.08 (1.02–1.14) and RR=1.12 (1.05–1.19), respectively, for distances between 10 and 30 km, 30 and 50 km and 50 and 70 km, P-trend=0.024) (n=28 010 and n=18 080, respectively) but was not significant for gall bladder and biliary tract cancer (n=2893) or small intestine cancer (n=1038). Even though the influence of socioeconomic status on prognosis is modest compared to clinical prognostic factors such as histology or stage at diagnosis, socioeconomic deprivation and distance to nearest cancer centre need to be considered as potential survival predictors in digestive tract cancer
Superconductivity in Ropes of Single-Walled Carbon Nanotubes
We report measurements on ropes of Single Walled Carbon Nanotubes (SWNT) in
low-resistance contact to non-superconducting (normal) metallic pads, at low
voltage and at temperatures down to 70 mK. In one sample, we find a two order
of magnitude resistance drop below 0.55 K, which is destroyed by a magnetic
field of the order of 1T, or by a d.c. current greater than 2.5 microA. These
features strongly suggest the existence of superconductivity in ropes of SWNT.Comment: Accepted for publication in Phys. Rev. Let
Superconductivity in carbon nanotube ropes
We investigate the conditions in which superconductivity may develop in ropes
of carbon nanotubes. It is shown that the interaction among a large number of
metallic nanotubes favors the appearance of a metallic phase in the ropes,
intermediate between respective phases with spin-density-wave and
superconducting correlations. These arise in samples with about 100 metallic
nanotubes or more, where the long-range Coulomb interaction is very effectively
reduced and it may be overcome by the attractive interaction from the exchange
of optical phonons within each nanotube. We estimate that the probability for
the tunneling of Cooper pairs between neighboring nanotubes is much higher than
that for single electrons in a disordered rope. The effect of pair hopping is
therefore what establishes the intertube coherence, and the tunneling amplitude
of the Cooper pairs dictates the scale of the transition to the superconducting
state.Comment: 12 page
Testosterone Therapy in Adult-Onset Testosterone Deficiency: Hematocrit and Hemoglobin Changes
Objective: Hematocrit (HCT)/hemoglobin (Hb) ratio in (%/g/dL) is around 3, with high fidelity between measured
and derived Hb (applying the conversion using HCT) in various pathologies. We examined changes in
HCT and Hb values and HCT/Hb, compared with baseline, in men with adult-onset testosterone deficiency
(TD) given testosterone therapy (TTh).
Materials and Methods: Data were analyzed from an observational, prospective registry study at various time
points in 353 men with adult-onset TD receiving testosterone undecanoate (median follow-up: 105 months).
After establishing baseline HCT/Hb, we compared (cf. baseline) changes in HCT, Hb, and HCT/Hb at 12, 48, 72,
and 96 months. Regression analyses determined predictors of HCT and Hb change.
Results: TTh was associated with ( p < 0.0001) increases in median HCT and Hb; 44% to 49% and 14.5 to 14.9 g/dL
at final assessment, respectively. Regression analyses showed that HCT change was associated with baseline HCT
and testosterone levels, while Hb change was associated with baseline Hb, HCT, and testosterone levels. In the
total cohort and subgroups, HCT/Hb increased significantly at all time points ( p < 0.0001, cf. baseline) with over
90% of men demonstrating increases. Linear regression showed that the ratio of HCT change/Hb change (i.e.,
difference between HCT at the various time points and baseline value/difference between Hb at the various
time points and baseline value), following TTh at each time point was higher than the baseline HCT/Hb ratio.
Conclusion: HCT increase was greater than we anticipated from the established HCT/Hb of 3. We speculate that
increased erythrocyte life span with associated higher Hb loss via vesiculation could account for our observation.
This could have a bearing when using HbA1c as an indicator in men with adult-onset TD on TTh
- …