We report a new chemical vapor synthesis method that exploits random fluctuations in the viscous boundary layer between a laminar vapor flow and a surface to yield a not previously observed product: ...radial ferromagnetically filled-carbon-nanotube structures departing from a central particle. The filling of the nanotube capillary is continuous over a scale much greater than that which can be achieved by conventional CVD. This is a simple method which does not require ultra-fine control of process parameters or highly-engineered reactor components in which a single, self-organized, ordered product is formed in randomly fluctuating vapor in the boundary layer by vapor-, liquid-, solid-phase self-organization. These fluctuations create the thermodynamic conditions for formation of the central particle in the vapor which in turn defines the spherically symmetric diffusion gradient that initiates the radial growth. The subsequent radial growth is driven by the supply of vapor feedstock by local diffusion gradients created by endothermic graphitic carbon formation at the vapor-facing tips of the individual nanotubes and is halted by contact with the surface. The radial structures are the dominant product and the reaction conditions are self-sustaining. We argue that the method has potential for scalable production of metal-carbon nanostructures with other unusual morphologies.
Observation of superconductivity in twisted-bilayer-graphene and highly-oriented-pyrolytic-graphite (HOPG) for certain magic-angles-of-rotation has recently attracted an important attention. Unusual ...temperature-(T)-induced-shifts in the graphitic c-axis have also been reported in HOPG in conditions of θmisfit ∼ 1° (first-magic-angle).
We report a novel investigation of HOPGs with θmisfit of 0.5°, 0.8°, 1.5°, ≫ 1.5° and of water-treated-turbostratic-graphite in the T-range from 298.15 to 673.15K. Presence of magic angles of rotations corresponding to the reported θmisfit values is demonstrated by repeated HRTEM and Moiré pattern analyses of HOPG lamellae extracted from individual samples with scotch tape methods. Interestingly in our measurements the c-axis-shift is found to depend strongly on the misfit-angle, with the highest-values of 0.00428 and 0.00426 nm in proximity of the first-magic-angle (θmisfit ∼ 0.8° and ∼0.5°). Two diffraction-peaks present at ∼23.5° and ∼48.5° 2θ (detector angle, in typical Bragg- Brentano configuration) for θmisfit ∼1° are also found to vanish for θmisfit ≫ 1.5°. These findings imply existence of additional symmetry elements at the magic angle, which are not present in the standard space group notation used for structural characterization of graphite (P63/mmc).
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Large-scale transport is investigated in terms of new explicit expressions for eddy diffusivities and effective advection obtained from asymptotic perturbative methods. The carrier flow is formed by ...a large-scale component plus a small-scale contribution mimicking a turbulent flow. The scalar dynamics is observed in its pre-asymptotic regimes (i.e. on scales comparable to those of the large-scale velocity). The resulting eddy diffusivity is thus a tensor field which explicitly depends on the large-scale velocity. Small-scale interactions also cause the emergence of an effective large-scale (compressible) advection field which, as a result of the present study however, turns out to be of negligible importance. Two issues are addressed by means of Lagrangian simulations: quantifying the possible deterioration of the eddy-diffusivity/effective advection description by reducing to zero the spectral gap separating the large-scale velocity component from the small-scale component; comparing the accuracy of our closure against other simple, reasonable, options. Answering these questions is important in view of possible applications of our closure to tracer dispersion in environmental flows.
Introduction
The role of cannabis on cognitive impairment in first-episode psychosis (FEP) is becoming more important, with multiple investigations on this regard, with heterogeneous results due to ...different methodologies.
Objectives
To evaluate the cognitive profile in patients who suffer a FEP, analyzing the potential effect of cannabis.
Methods
We present the preliminar results of a cross-sectional case-control study about the effect of cannabis on cognition, in patients suffering a FEP. We recruited a total of 41 FEP during the last two years. We investigated the theorical differences between those who were cannabis users (FEP-Cannabis+)(n=28) and not cannabis users (FEP-Cannabis-)(n=13). We included a control group with healthy subjects who were cannabis users (Healthy-Cannabis+)(n=24).Sociodemographic and clinical questionnaire was completed. The Screening Scale to evaluate Cognitive Impairment in Psychiatry(SCIP-S) and the Cannabis Abuse Screening Test (CAST) were used. The consumption pattern was also evaluated.
Results
In this study, cognitive impairment was found in FEP-Cannabis+,when compared with Healthy-Cannabis+.The most affected areas were immediate verbal learning (I-VL), delayed verbal learning (D-VL), processing speed (PS), and total score (TS). Significant differences were also observed in the cognitive profile of patients suffering FEP depending on their use of cannabis. FEP-Cannabis+) showed lower scores in PS, I-VL and TS.
Conclusions
Although several prognostic factors have been identified in FEP, to date there are no reliable markers for predicting the possible evolution of high-risk mental states to a FEP. More investigations are necessary in order to elucidate the role of cannabis in the cognitive impairment.
Disclosure
No significant relationships.
We report a novel structural and magnetic investigation of carbon foam (CFM) materials filled with SmFeO3 crystals produced by (1) high temperature fusion between Sm2O3- and Fe3C-filled carbon onions ...and (2) annealing of iron filled CFM with nanosized Sm2O3. Presence of a defect-rich monolayer-like CFM arrangement characterized by sharp interfaces with a SmFeO3 single-crystal phase is demonstrated through TEM and HRTEM. Further, the presence of intense sp3-rich features with variable carbonate content is evidenced by XPS and Raman spectroscopy. Complementary VSM, SQUID and ESR show also presence of intrinsic magnetization features which appeared to be attributable to the interfacial vacancy-rich regions of the graphitic CFM layers, as confirmed by Raman spectroscopy. Together with these signals, possible ferromagnetic contributions from the SmFeO3 phase and α-Fe impurities are reported. These observations highlight therefore the presence of switchable interfacial magnetization features at the carbon/SmFeO3 interface due to the variable concentrations of vacancies at the CFM interface, opening new directions towards applications in magnetic and interfacial-driven ferroelectric devices.
Carbon nanotubes filled with continuous crystalline nanowires of nanometre-scale diameter and micrometre-scale length of the ferromagnetic phase α-Fe were produced with a new chemical vapour ...deposition method. We report a new two-stage approach, a perturbed-vapour method of synthesis followed by a post-synthesis heat treatment that produces multiwall carbon nanotubes filled with at least 19 micrometre-length nanowires of α-Fe. Previously reported synthesis routes use steady-state conditions to guarantee nanowire continuity but result only in small (less than one-micrometre length) nanowires comprising isolated or mixed phases of either α-Fe, Fe3C, or γ-Fe. Here flower-like clusters of carbon nanotubes continuously filled with α-Fe were produced by perturbation of a laminar ferrocene (Fe(C5H5)2) vapour flow in a conventional horizontal chemical vapour deposition reactor. Single-phase filling was achieved by a post-synthesis annealing at 500°C for 15h in Ar flow. Electron microscopy studies revealed the high quality of the structural integrity of both nanotubes and encapsulated nanowires. These nanostructures possess a high coercivity of 580Oe and a very high saturation magnetization of 189.5emu/g comparable with bulk α-Fe.
Occurrence of magnetic-correlation-phenomena in multi-layered carbon-materials has recently attracted an important attention for applications in magnetic devices and spintronics. In this study, ...exfoliated highly-oriented-pyrolytic-graphite (HOPG) lamellae exhibiting hexagonal-Moiré-superlattices, with periodicity of ∼13 nm (1st category, θrot ∼ 1.09° ) and ∼36 nm (2nd category, θrot ∼ 0.39°) were investigated. Raman-spectroscopy evidenced weak D, D' and intense G bands. In 1st category, magnetization versus field, ZFC- FC magnetic-curves from 2 K to 300 K and T-ESR revealed presence of uncorrelated and correlated ferromagnetic clusters at T* ∼ 150 K together with a critical transition at Tc ∼ 50 K, compatible with percolative-ferromagnetic-correlation. Comparative measurements on the 2nd category, revealed an analogue trend, with at T* ∼ 50-60 K together with an irreversibility at Tc ∼ 40 K, indicative of competing ferromagnetic/antiferromagnetic-correlations.
We report a novel T-XRD and Rietveld-refinement investigation of pyrolytic-graphite samples with high degree of graphene-layer-orientation and misfit-rotational-angle of ∼0.8° in the T-range from 12 ...K to 298 K. An anomalous variation of the graphitic c-axis which involves firstly negative-thermal-expansion (from 12 K to ∼50 K), a saturation-effect (from 50 K to ∼160 K) and then a positive expansion (from ∼180 K to 298 K) is evidenced. The reported trend is significantly different with respect to that expected by considering the standard-thermal-expansion -parameter where no saturation-effect is present. SQUID-magnetometry revealed further presence of superconducting-like hysteresis which resemble those observed by Scheike et al.
We report the observation of novel temperature-driven structural-memory-effects in carbon nanotubes (CNTs) filled with Fe3C nano-crystals. These structural-transitions were measured by means of ...temperature (T) dependent x-ray diffraction (XRD) in the T-range from 298 K to 12 K. A clear reversible 2θ-shift in the 002-peak of the graphitic-CNTs-walls is found with the decrease of the temperature. As determined by Rietveld refinement, such 2θ-shift translates in a not previously reported decrease in the value of the CNT graphitic c-axis with the decrease of the temperature (from 298 K to 12 K). Also, a clear reversible 2θ-shift in the 031 and 131 diffraction-peaks of Fe3C is observed within the same T-range. Rietveld refinements confirm the existence of such memory-effect and also reveal a gradual decrease of the 010-axis of Fe3C with the decrease of the temperature. These observations imply that the observed structural-memory-effect is a characteristic of CNTs when Fe3C is the encapsulated ferromagnet. The generality of such memory-effects was further confirmed by additional measurements performed on other types of CNTs characterized by continuous Fe3C-filling. XRD measurements in the T-range from 298 K to 673 K revealed also an unusual reversible decrease of the Fe3C-peak intensities with the increase of the temperature. These observations can have important implications on the magnetic data recording applications of these nanostructures by helping in better understanding the unusual temperature-dependent magnetic instabilities of iron-based nano-crystals which have been recently reported in literature.
Abstract
After its successful campaign of measurements beyond the Polar Arctic Circle, the PolarquEEEst experiment measured the cosmic charged particle rate at sea level in a latitude interval ...between 35
$$^{\circ }$$
∘
N and 82
$$^{\circ }$$
∘
N. In this paper, these measurements are described and the corresponding results are discussed.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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