42 research outputs found
Turbulent convection at very high Rayleigh numbers and the weakly nonlinear theory
To provide insights into the challenging problem of turbulent convection,
Jack Herring used a greatly truncated version of the complete Boussinesq
equations containing only one horizontal wavenumber. In light of later
observations of a robust large scale circulation sweeping through convecting
enclosures at high Rayleigh numbers, it is perhaps not an implausible point of
view from which to reexamine high-Rayleigh-number data. Here we compare past
experimental data on convective heat transport at high Rayleigh numbers with
predictions from Herring's model and, in fact, find excellent agreement. The
model has only one unknown parameter compared to the two free parameters
present in the lowest order least-squares power-law fit. We discuss why the
underlying simplistic physical picture, meant to work at Rayleigh numbers
slightly past the critical value of a few thousands, is consistent with the
data, when the single free parameter in it is revised, over some eleven decades
of the Rayleigh number -- stretching from about a million to about
24 mJ Cr+4:forsterite four-stage master-oscillator power-amplifier laser system for high resolution mid-infrared spectroscopy
We present the design of a Cr:forsterite based single-frequency master-oscillator power-amplifier laser system delivering much higher output energy compared to previous literature reports. The system has four amplifying stages with two-pass configuration each, thus enabling the generation of 24 mJ output energy in the spectral region around 1262 nm. It is demonstrated that the presented Cr:forsterite amplifier preserves high spectral and pulse quality, allowing a straightforward energy scaling. This laser system is a promising tool for tunable nonlinear down-conversion to the mid-infrared spectral range and will be a key building block in a system for high-resolution muonic hydrogen spectroscopy in the 6.8 \u3bcm rang
Dense Plasma Focus: physics and applications (radiation material science, single-shot disclosure of hidden illegal objects, radiation biology and medicine, etc.)
The paper presents some outcomes obtained during the year of 2013 of the activity in the frame of the International Atomic Energy Agency Co-ordinated research project "Investigations of Materials under High Repetition and Intense Fusion-Relevant Pulses". The main results are related to the effects created at the interaction of powerful pulses of different types of radiation (soft and hard X-rays, hot plasma and fast ion streams, neutrons, etc. generated in Dense Plasma Focus (DPF) facilities) with various materials including those that are counted as perspective ones for their use in future thermonuclear reactors. Besides we discuss phenomena observed at the irradiation of biological test objects. We examine possible applications of nanosecond powerful pulses of neutrons to the aims of nuclear medicine and for disclosure of hidden illegal objects. Special attention is devoted to discussions of a possibility to create extremely large and enormously diminutive DPF devices and probabilities of their use in energetics, medicine and modern electronics
Shared Genetic Risk Factors of Intracranial, Abdominal, and Thoracic Aneurysms
Background-Intracranial aneurysms (IAs), abdominal aortic aneurysms (AAAs), and thoracic aortic aneurysms (TAAs) all have a familial predisposition. Given that aneurysm types are known to co-occur, we hypothesized that there may be shared genetic risk factors for IAs, AAAs, and TAAs. Methods and Results-We performed a mega-analysis of 1000 Genomes Project-imputed genome-wide association study (GWAS) data of 4 previously published aneurysm cohorts: 2 IA cohorts (in total 1516 cases, 4305 controls), 1 AAA cohort (818 cases, 3004 controls), and 1 TAA cohort (760 cases, 2212 controls), and observed associations of 4 known IA, AAA, and/or TAA risk loci (9p21, 18q11, 15q21, and 2q33) with consistent effect directions in all 4 cohorts. We calculated polygenic scores based on IA-, AAA-, and TAA-associated SNPs and tested these scores for association to case-control status in the other aneurysm cohorts; this revealed no shared polygenic effects. Similarly, linkage disequilibrium-score regression analyses did not show significant correlations between any pair of aneurysm subtypes. Last, we evaluated the evidence for 14 previously published aneurysm risk single-nucleotide polymorphisms through collaboration in extended aneurysm cohorts, with a total of 6548 cases and 16 843 controls (IA) and 4391 cases and 37 904 controls (AAA), and found nominally significant associations for IA risk locus 18q11 near RBBP8 to AAA (odds ratio [OR]= 1.11; P=4.1 x 10(-5)) and for TAA risk locus 15q21 near FBN1 to AAA (OR=1.07; P=1.1 x 10(-3)). Conclusions-Although there was no evidence for polygenic overlap between IAs, AAAs, and TAAs, we found nominally significant effects of two established risk loci for IAs and TAAs in AAAs. These two loci will require further replication.Peer reviewe
Communicating Science Worldwide with the UNESCO International Day of Light
International audience<span style="color: black;">For over ten years, a global partnership of scientific societies and other organizations has worked with the United Nations Educational and Scientific Organization (UNESCO) to raise awareness amongst broad audiences of the importance of science for sustainable development, structured around the particular theme of light science and optical technologies. This partnership led to the proclamation of the year 2015 as the United Nations International Year of Light, and the recognition since 2018 of an annual UNESCO International Day of Light, celebrated every year on May 16. This contribution reviews these international actions and will describe a number of lessons that have been learned, not only about how to communicate to the public at large, but also the parallel (and in many ways more difficult) problem of science communication to decision-makers. <br></span&g
Thermal lensing approach based on parabolic approximation and Mach-Zehnder interferometer
A thermal lensing approach based on parabolic approximation and Mach-Zehnder interferometer for measuring optical absorption and thermal diffusivity coefficients in pure solvents is described in this work. The approach combines the sensitivity of both thermal lensing methods and interferometry techniques. The photothermal effect is induced by a pump laser beam generating localized changes in the refractive index of the sample, which are observed as a shift in phase of the interference pattern. Each interference pattern is recorded by means of a digital camera and stored as digital images as a function of time. The images are then numerically processed to calculate the phase shifting map for a specific time. From each phase shifting map, the experimental phase difference as a function of time is calculated giving a phase-time transient, which is fitted to a mathematical model to estimate the optical absorption and thermal diffusivity of the sample. The experimental results show that the sensitivity is approximately λ/4800 for the minimum phase difference measured