Variable repetition frequency asynchronous optical sampling method without a feedback loop

Nagakubo A., Kanai K., Tamura H., et al. Variable repetition frequency asynchronous optical sampling method without a feedback loop. AIP Advances 12, 045323 (2022); https://doi.org/10.1063/5.0083354.The ultrafast pump-probe measurement represents a key technique to study fs-ps dynamics. The asynchronous optical sampling (ASOPS) method realizes fast and long time-range measurement with high time resolution using different repetition frequency pump-probe light pulses. The frequency difference Δf is an important parameter, as it dictates the measurement time and time resolution. However, usual ASOPS measurements require a complex and precise stabilizer to control Δf or it is difficult to change Δf. In this study, we use two free-running titanium/sapphire pulse lasers to develop a variable repetition frequency ASOPS (VRF-ASOPS) method without a stabilizer or feedback loop, where we can easily alter Δf by changing the cavity length of the probe light laser. To detect the coincidences of the pump-probe light pulses, we cause the instantaneous reflectivity change in a 100 nm platinum film by irradiating the pump light and observe it by the probe light. We use this signal as the trigger signal to directly determine Δf, which enables us to average and convert the measured responses without a stabilizer or feedback loop. Using this VRF-ASOPS system, we obtain pulse echo signals and 100 GHz Brillouin oscillations, which are equivalent to those measured by the mechanical delay line method, confirming the validity of our developed method

ClaimChain: Improving the Security and Privacy of In-band Key Distribution for Messaging

The social demand for email end-to-end encryption is barely supported by mainstream service providers. Autocrypt is a new community-driven open specification for e-mail encryption that attempts to respond to this demand. In Autocrypt the encryption keys are attached directly to messages, and thus the encryption can be implemented by email clients without any collaboration of the providers. The decentralized nature of this in-band key distribution, however, makes it prone to man-in-the-middle attacks and can leak the social graph of users. To address this problem we introduce ClaimChain, a cryptographic construction for privacy-preserving authentication of public keys. Users store claims about their identities and keys, as well as their beliefs about others, in ClaimChains. These chains form authenticated decentralized repositories that enable users to prove the authenticity of both their keys and the keys of their contacts. ClaimChains are encrypted, and therefore protect the stored information, such as keys and contact identities, from prying eyes. At the same time, ClaimChain implements mechanisms to provide strong non-equivocation properties, discouraging malicious actors from distributing conflicting or inauthentic claims. We implemented ClaimChain and we show that it offers reasonable performance, low overhead, and authenticity guarantees.Comment: Appears in 2018 Workshop on Privacy in the Electronic Society (WPES'18

Contribution of socioeconomic status, stature and birth weight to obesity in Sub-Saharan Africa: cross-sectional data from primary school-age children in Cameroon

Background: The pattern of obesity in relation to socioeconomic status is of public health concern. This study investigates whether the association between height and obesity in children is affected by their socioeconomic background. It also explores the relationship between high birth weight and obesity. Methods: School children, (N = 557; 5 to 12 years old) were recruited from randomly selected primary schools in a cross-sectional study including 173 rural and 384 urban children in the North West Region of Cameroon. Socioeconomic status (SES) and birth weight were obtained using a self administered questionnaire. Anthropometric measures included height, weight, BMI, waist circumference and percentage body fat. These measures were transformed into age and sex-standardized variables. Then participants were divided according to quartiles of height SDS. Results: The highest frequencies of overweight/obesity (18.8%), abdominal overweight/obesity (10.9%) and high body fat/obesity (12.3%) were observed among the tallest children from a high socioeconomic background. Univariate analyses indicate that children of high SES (39.9%), fourth height quartile (33.1%) and of high birth weight (54.8%) were significantly (p<0.001) more likely to be overweight/obese. Multivariate analyses showed high SES (OR 8.3, 95% CI 3.9 - 15.4), fourth height quartile (OR 9.1, 95% CI 3.4 - 16.7) and high birth weight (OR 0.1, 95% CI 0.06 - 0.2) as independent predictors of overweight/obesity. Conclusions: This study confirms that children coming from a high socioeconomic background and being tall are at particular risk of becoming obese

High-precision CTE measurement of hybrid C/SiC composite for cryogenic space telescopes

This paper presents highly precise measurements of thermal expansion of a "hybrid" carbon-fiber reinforced silicon carbide composite, HB-Cesic\textregistered - a trademark of ECM, in the temperature region of \sim310-10K. Whilst C/SiC composites have been considered to be promising for the mirrors and other structures of space-borne cryogenic telescopes, the anisotropic thermal expansion has been a potential disadvantage of this material. HB-Cesic\textregistered is a newly developed composite using a mixture of different types of chopped, short carbon-fiber, in which one of the important aims of the development was to reduce the anisotropy. The measurements indicate that the anisotropy was much reduced down to 4% as a result of hybridization. The thermal expansion data obtained are presented as functions of temperature using eighth-order polynomials separately for the horizontal (XY-) and vertical (Z-) directions of the fabrication process. The average CTEs and their dispersion (1{\sigma}) in the range 293-10K derived from the data for the XY- and Z-directions were 0.805$\pm$0.003\times10$^{-6}$ K$^{-1}$ and 0.837\pm0.001\times10$^{-6}$ K$^{-1}$, respectively. The absolute accuracy and the reproducibility of the present measurements are suggested to be better than 0.01\times10$^{-6}$ K$^{-1}$ and 0.001\times(10)^{-6} K^{-1}, respectively. The residual anisotropy of the thermal expansion was consistent with our previous speculation regarding carbon-fiber, in which the residual anisotropy tended to lie mainly in the horizontal plane.Comment: Accepted by Cryogeincs. 12 pages, 3 figures, 1 tabll

Effectiveness of conservation measures to support biodiversity in boreal timber-production forests

Large parts of the boreal forest ecosystems have been greatly affected by human use, and the current timber-oriented forest management practice that dominates boreal forests is proven to cause biodiversity and ecosystem services declines. These negative effects are mitigated in various ways, including in-situ measures implemented upon harvest. The measures comprise trade-offs between economic and ecological aims; thus, requiring solid knowledge of their effectiveness. However, comprehensive literature review of the effectiveness of such measures is scarce. We aim to fill part of this void by reviewing the scientific literature that have gauged effects of four in-situ conservation measures: green tree retention (GTR), patch retention (PR), dead wood retention (DW) and riparian buffer zones (RB). Two outcomes were considered, species richness and species abundance across taxa. From a total of 3012 initial papers, 48 met our inclusion criteria that generated 238 unique results. Results were grouped according to control. 178 studies used mature, unlogged forest as control. Out of those, 68% of the findings were not significant, i.e., suggesting no significant impact of harvest with biodiversity measures on species richness and species abundance compared to no harvest. Eighteen percent of the observations showed negative effects and 14% of the observations showed positive effects compared to no harvest. Sixty studies used harvest with no measures as control, of which 45% showed significant positive effects, meaning that compared to harvest with no measures, harvest with conservation measures has positively effects on species richness and abundance. However, 43% of the studies found no significant effect of the implemented conservation measures compared to harvest with no measures taken. The relatively few significant results reported restrain distinct conclusions on the effectiveness of the assessed conservation measures, but some degree of conservation measure is likely to have positive effects on biodiversity in timber-production forest. However, the scientific basis does not allow for pointing to threshold levels. Higher transparency of study design and statistical results would allow us to include more studies. There is a clear need for more research of effectiveness of common conservation measures in timber-production forests in order to strengthen the knowledge basis. In particular, there are few studies that employ harvest without any conservation measure as control. This is pivotal knowledge for forest managers as well as for policymakers for preserving biodiversity and the ecosystems in forest

Multi-wavelength analysis of 18um-selected galaxies in the AKARI/IRC monitor field towards the North Ecliptic Pole

We present an initial analysis of AKARI 18um-selected galaxies using all 9 photometric bands at 2-24um available in the InfraRed Camera (IRC), in order to demonstrate new capabilities of AKARI cosmological surveys. We detected 72 sources at 18um in an area of 50.2 arcmin^2 in the AKARI/IRC monitor field towards the North Ecliptic Pole (NEP). From this sample, 25 galaxies with probable redshifts z>~ 0.5 are selected with a single colour cut (N2-N3>0.1) for a detailed SED analysis with ground-based BVRi'z'JK data. Using an SED radiative transfer model of starbursts covering the wavelength range UV -- submm, we derive photometric redshifts from the optical-MIR SEDs of 18um-selected galaxies. From the best-fit SED models, we show that the IRC all-band photometry is capable of tracing the steep rise in flux at the blue side of the PAH 6.2um emission feature. This indicates that the IRC all-band photometry is useful to constrain the redshift of infrared galaxies, specifically for dusty galaxies with a less prominent 4000A break. Also, we find that the flux dip between the PAH 7.7 and 11.2um emission feature is recognizable in the observed SEDs of galaxies at z~1. By using such a colour anomaly due to the PAH and silicate absorption features, unique samples of ULIRGs at z~1, `silicate-break' galaxies, can be constructed from large cosmological surveys of AKARI towards the NEP, i.e. the NEP-Deep and NEP-Wide survey. This pilot study suggests the possibility of detecting many interesting galaxy properties in the NEP-Deep and Wide surveys, such as a systematic difference in SEDs between high- and low-z ULIRGs, and a large variation of the PAH inter-band strength ratio in galaxies at high redshifts. [abridged]Comment: Accepted for publication in PASJ, AKARI special issu

Planar shock wave generated by uniform irradiation from two overlapped partially coherent laser beams

Copyright 2001 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics, 89(5), 2571-2575, 2001 and may be found at http://dx.doi.org/10.1063/1.134218

Electrons in High-Tc Compounds: Ab-Initio Correlation Results

Electronic correlations in the ground state of an idealized infinite-layer high-Tc compound are computed using the ab-initio method of local ansatz. Comparisons are made with the local-density approximation (LDA) results, and the correlation functions are analyzed in detail. These correlation functions are used to determine the effective atomic-interaction parameters for model Hamiltonians. On the resulting model, doping dependencies of the relevant correlations are investigated. Aside from the expected strong atomic correlations, particular spin correlations arise. The dominating contribution is a strong nearest neighbor correlation that is Stoner-enhanced due to the closeness of the ground state to the magnetic phase. This feature depends moderately on doping, and is absent in a single-band Hubbard model. Our calculated spin correlation function is in good qualitative agreement with that determined from the neutron scattering experiments for a metal.Comment: 21pp, 5fig, Phys. Rev. B (Oct. 98