Simulation of dimensionality effects in thermal transport

The discovery of nanostructures and the development of growth and fabrication techniques of one- and two-dimensional materials provide the possibility to probe experimentally heat transport in low-dimensional systems. Nevertheless measuring the thermal conductivity of these systems is extremely challenging and subject to large uncertainties, thus hindering the chance for a direct comparison between experiments and statistical physics models. Atomistic simulations of realistic nanostructures provide the ideal bridge between abstract models and experiments. After briefly introducing the state of the art of heat transport measurement in nanostructures, and numerical techniques to simulate realistic systems at atomistic level, we review the contribution of lattice dynamics and molecular dynamics simulation to understanding nanoscale thermal transport in systems with reduced dimensionality. We focus on the effect of dimensionality in determining the phononic properties of carbon and semiconducting nanostructures, specifically considering the cases of carbon nanotubes, graphene and of silicon nanowires and ultra-thin membranes, underlying analogies and differences with abstract lattice models.Comment: 30 pages, 21 figures. Review paper, to appear in the Springer Lecture Notes in Physics volume "Thermal transport in low dimensions: from statistical physics to nanoscale heat transfer" (S. Lepri ed.

The views and experiences of suicidal children and young people of mental health support services: A meta-ethnography.

Background: Suicide is amongst the leading causes of death in young people globally and a health priority worldwide. For children and young people (CYP) attempting or considering suicide there is no agreed treatment model. Development of treatment models should be informed by the views and experiences of CYP using services. Methods: Meta-ethnography was used to systematically identify and synthesise studies reporting the views of CYP who used mental health services following suicidal behaviour. Relevant studies were quality appraised. First order (participants) and second order (original author) data were translated to identify common and disconfirming themes and concepts. Translated findings were synthesised and led to a new hypothesis supported by additional ‘linguistic analysis’ of texts to construct a novel third order line-of-argument. Results: Four studies conducted since 2006 in three countries involving 44 young people aged 11-24 years were synthesised. Translation revealed that suicidal CYP do not know where or how to access help, they cannot access help directly and when seen by mental health practitioners they do not feel listened to. Line-of-argument synthesis identified a silence around suicidality within the conversations CYP have with mental health practitioners and within academic research reporting. Use of the term ‘self-harm’ to encompass suicidal behaviours potentially contributes to this silence by avoiding the word ‘suicide’. Conclusions: CYP who are suicidal need to have easy access to mental health services. When using services, they want to feel listened to and have suicidal feelings acknowledged. This involves professionals referring explicitly to suicide not just self-harm

Engagement of vulnerable youths using Internet platforms

Survey data of 1010 participants exploring their internet usage preference and their willingness to be engaged by online professionals if they are in need. Abstract Aim: Our study aims to understand youths’ online behavior in terms of disclosing their distress and help seeking. Methods: A cross-sectional telephone-based survey was conducted with 1,010 young people in Hong Kong. Logistic regression analysis was conducted to identify the factors associated with youths who express emotional distress online and the differences among four categories of youths—non-distressed youths (reference group) and three categories of distressed youths (not-seek-help group, sought informal help, and sought formal help groups)—in terms of their help seeking behavior. Results: Those who expressed distress online were associated with a higher lifetime prevalence of suicidal ideation. The active informal help group had a risk profile similar to that of the inactive group, including suicide risk, unsafe sex, and being bullied. The active informal help group tended to express distress online, which indicates that they may be more accessible for professionals to identify. More importantly, approximately 20% of the distressed youths did not seek formal or informal help yet expressed their distress online. Implication: The results of this study indicate that there are opportunities for helping professionals to develop strategic engagement methods using social media to help distressed youths

Engagement of vulnerable youths using Internet platforms

Survey data of 1010 participants exploring their internet usage preference and their willingness to be engaged by online professionals if they are in need. Abstract Aim: Our study aims to understand youths’ online behavior in terms of disclosing their distress and help seeking. Methods: A cross-sectional telephone-based survey was conducted with 1,010 young people in Hong Kong. Logistic regression analysis was conducted to identify the factors associated with youths who express emotional distress online and the differences among four categories of youths—non-distressed youths (reference group) and three categories of distressed youths (not-seek-help group, sought informal help, and sought formal help groups)—in terms of their help seeking behavior. Results: Those who expressed distress online were associated with a higher lifetime prevalence of suicidal ideation. The active informal help group had a risk profile similar to that of the inactive group, including suicide risk, unsafe sex, and being bullied. The active informal help group tended to express distress online, which indicates that they may be more accessible for professionals to identify. More importantly, approximately 20% of the distressed youths did not seek formal or informal help yet expressed their distress online. Implication: The results of this study indicate that there are opportunities for helping professionals to develop strategic engagement methods using social media to help distressed youths

Theoretical and experimental investigations of optical, structural and electronic properties of the lower-dimensional hybrid [NH3-(CH2)10-NH3]ZnCl4

In the current study, a combination between theoretical and experimental studies has been made for the hybrid perovskite [NH3-(CH2)10-NH3]ZnCl4. The density functional theory (DFT) was performed to investigate structural and electronic properties of the tilted compound. A local approximation (LDA) and semi-local approach (GGA) were employed. The results are obtained using, respectively, the local exchange correlation functional of Perdew-Wang 92 (PW92) and semi local functional of Perdew-Burke-Ernzerhof (PBE). The optimized cell parameters are in good agreement with the experimental results. Electronic properties have been studied through the calculation of band structures and density of state (DOS), while structural properties are investigated by geometry optimization of the cell. Fritz-Haber-Institute (FHI) pseudopotentials were employed to perform all calculations. The optical diffuse reflectance spectra was mesured and applied to deduce the refractive index (n), the extinction coefficient (k), the absorption coefficient (α), the real and imaginary dielectric permittivity parts (εr,εi)) and the optical band gap energy Eg. The optical band gap energy value shows good consistent with that obtained from DFT calculations and reveals the insulating behavior of the material

Simulation of Dimensionality Effects in Thermal Transport

The discovery of nanostructures and the development of growth and fabrication techniques of one- and two-dimensional materials provide the possibility to probe experimentally heat transport in low-dimensional systems. Nevertheless measuring the thermal conductivity of these systems is extremely challenging and subject to large uncertainties, thus hindering the chance for a direct comparison between experiments and statistical physics models. Atomistic simulations of realistic nanostructures provide the ideal bridge between abstract models and experiments. After briefly introducing the state of the art of heat transport measurement in nanostructures, and numerical techniques to simulate realistic systems at atomistic level, we review the contribution of lattice dynamics and molecular dynamics simulation to understanding nanoscale thermal transport in systems with reduced dimensionality. We focus on the effect of dimensionality in determining the phononic properties of carbon and semiconducting nanostructures, specifically considering the cases of carbon nanotubes, graphene and of silicon nanowires and ultra-thin membranes, underlying analogies and differences with abstract lattice models