Pressure screening in the interior of primary shells in double-wall carbon nanotubes

The pressure response of double-wall carbon nanotubes has been investigated by means of Raman spectroscopy up to 10 GPa. The intensity of the radial breathing modes of the outer tubes decreases rapidly but remain observable up to 9 GPa, exhibiting a behavior similar (but less pronounced) to that of single-wall carbon nanotubes, which undergo a shape distortion at higher pressures. In addition, the tangential band of the external tubes broadens and decreases in amplitude. The corresponding Raman features of the internal tubes appear to be considerably less sensitive to pressure. All findings lead to the conclusion that the outer tubes act as a protection shield for the inner tubes whereas the latter increase the structural stability of the outer tubes upon pressure application.Comment: PDF with 15 pages, 3 figures, 1 table; submitted to Physical Review

Raman spectra of MgB2 at high pressure and topological electronic transition

Raman spectra of the MgB2 ceramic samples were measured as a function of pressure up to 32 GPa at room temperature. The spectrum at normal conditions contains a very broad peak at ~590 cm-1 related to the E2g phonon mode. The frequency of this mode exhibits a strong linear dependence in the pressure region from 5 to 18 GPa, whereas beyond this region the slope of the pressure-induced frequency shift is reduced by about a factor of two. The pressure dependence of the phonon mode up to ~ 5GPa exhibits a change in the slope as well as a "hysteresis" effect in the frequency vs. pressure behavior. These singularities in the E2g mode behavior under pressure support the suggestion that MgB2 may undergo a pressure-induced topological electronic transition.Comment: 2 figure

11^{11}B NMR study of pure and lightly carbon doped MgB2_2 superconductors

We report a $^{11}$B NMR line shape and spin-lattice relaxation rate ($1/(T_1T)$) study of pure and lightly carbon doped MgB$_{2-x}$C$_{x}$ for $x=0$, 0.02, and 0.04, in the vortex state and in magnetic field of 23.5 kOe. We show that while pure MgB$_2$ exhibits the magnetic field distribution from superposition of the normal and the Abrikosov state, slight replacement of boron with carbon unveils the magnetic field distribution of the pure Abrikosov state. This indicates a considerable increase of $H_{c2}^c$ with carbon doping with respect to pure MgB$_2$. The spin-lattice relaxation rate $1/(T_1T)$ demonstrates clearly the presence of a coherence peak right below $T_c$ in pure MgB$_2$, followed by a typical BCS decrease on cooling. However, at temperatures lower than $\approx 10$K strong deviation from the BCS behavior is observed, probably from residual contribution of the vortex dynamics. In the carbon doped systems both the coherence peak and the BCS temperature dependence of $1/(T_1T)$ weaken, an effect attributed to the gradual shrinking of the $\sigma$ hole cylinders of the Fermi surface with electron doping.Comment: 8 pages, 6 figures, submitted to Phys. Rev.

Thinking deep. Acting on top. Underground built heritage and its fringe as a community catalyst for local sustainable development : Exploratory cases from poland and greece

Underground Built Heritage (UBH) is a distinct class of cultural heritage providing a focal point for community pride and engagement to become a springboard for local sustainable development (LSD). This research aims to articulate how local UBH and its fringe serve as a facilitator of communal identity to mobilize community care towards social and economic development with less involvement from the state and the market actors. For this purpose, local (and less-conspicuous) cases of UBH are employed in Warsaw, Poland, and Volos, Greece, indicating the power of UBH to connect and engage local communities with places, triggering a momentum for a truly bottom-up action that pays less attention to market considerations and state support. The studied UBH sites have been discussed according to an established common framework, dealing with five main issues: (a) general context and status, (b) history, (c) users and management, (d) ecosystem services, and (e) introduction of the paradigm of living labs. The analysis was based on a thorough literature review and complemented by field observations and interviews. The results provide evidence for UBH as a potential facilitator of social and economic development. The case studies in Poland and Greece showed that local actors were involved in activities and social networks of tacit knowledge, generating community building to reinforce bottom-up activities in contact with UBH

Synthesis of monoclinic Celsian from coal fly ash by using a one-step solid-state reaction

Monoclinic (Celsian) and hexagonal (Hexacelsian) Ba1−xSrxAl2Si2O8 solid solutions, where x = 0, 0.25, 0.375, 0.5, 0.75 or 1, were synthesized by using Coal Fly Ash (CFA) as main raw material, employing a simple one-step solid-state reaction process involving thermal treatment for 5 h at 850–1300 °C. Fully monoclinic Celsian was obtained at 1200 °C/5 h, for SrO contents of 0.25 ≤ x ≤ 0.75. However, an optimum SrO level of 0.25 ≤ x ≤ 0.375 was recommended for the stabilization of Celsian. These synthesis conditions represent a significant improvement over the higher temperatures, longer times and/or multi-step processes needed to obtain fully monoclinic Celsian, when other raw materials are used for this purpose, according to previous literature. These results were attributed to the role of the chemical and phase constitution of CFA as well as to a likely mineralizing effect of CaO and TiO2 present in it, which enhanced the Hexacelsian to Celsian conversion

Evaluating the efficacy of wearable biofeedback on the outcomes of exercise interventions in people with chronic non-specific spinal pain: protocol for a systematic review and meta-analysis

Introduction Wearable neuromuscular and biomechanical biofeedback technology has the potential to improve patient outcomes by facilitating exercise interventions. We will conduct a systematic review to examine whether the addition of wearable biofeedback to exercise interventions improves pain, disability and quality of life beyond exercise alone for adults with chronic non-specific spinal pain. Specific effects on clinical, physiological, psychological, exercise adherence and safety outcomes will also be examined. Methods and analysis A systematic search will be conducted from inception to February 2024. Full articles in the English language will be included. MEDLINE, PubMed, CINAHL, EMBASE, Web of Science, PsycINFO, AMED, SPORTDiscus, CENTRAL databases, clinical trial registries and ProQuest (PQDT) will be used to search for eligible studies. Grey literature and conference proceedings (2022–2024) will be searched for relevant reports. Randomised controlled trials using wearable neuromuscular or kinematic biofeedback devices as an adjunct to exercise interventions for the treatment of chronic spinal pain will be included in this systematic review. The comparators will be wearable biofeedback with exercise versus exercise alone, or wearable biofeedback with exercise versus placebo and exercise. Risk of bias will be assessed using Cochrane Back Review Group criteria and the quality of evidence using Grading of Recommendations Assessment, Development and Evaluation recommendations. Ethics and dissemination The systematic review will be based on published studies, and therefore, does not require ethical approval. The study results will be submitted for publication in an international, open-access, peer-reviewed journal and shared through conferences and public engagement. PROSPERO registration number CRD42023481393

Superconductivity: Exotic Commonalities in Phase and Mode

Recent muon and neutron experiments on the new FeAs-based superconductors revealed phase diagrams characterized by first-order evolution from antiferromagnetic to superconducting states, and an inelastic magnetic resonance mode whose energy scales as $\sim 4 k_{B}T_{c}$. These features exhibit striking commonalities with cuprate, backyball, organic, and heavy-fermion superconductors as well as superfluid $^{4}$He.Comment: 4 pages, 2 figures, original version of News and Views for Nature Materials submitted on Feb. 8, 2009; revised version will appear as Nature Materials 8 (April, 2009) 253-25

muSR study of carbon-doped MgB2 superconductors

The evolution of the superconducting properties of the carbon-doped MgB2 superconductors, MgB(2-x)Cx (x= 0.02, 0.04, 0.06) have been investigated by the transverse-field muon spin rotation (TF-muSR) technique. The low-temperature depolarisation rate, sigma(0) at 0.6 T which is proportional to the second moment of the field distribution of the vortex lattice decreases monotonically with increasing electron doping and decreasing Tc. In addition, the temperature dependence of sigma(T) has been analysed in terms of a two-gap model. The size of the two superconducting gaps decreases linearly as the carbon content increases, while the doping effect is more pronounced for the smaller gap related to the 3D pi-sheets of the Fermi surface.Comment: 7 pages, 2 Figures, 1 Table, Europhys. Lett. in pres