Surface roughness during depositional growth and sublimation of ice crystals

Full version of an earlier discussion paper (Chou et al. 2018)Ice surface properties can modify the scattering properties of atmospheric ice crystals and therefore affect the radiative properties of mixed-phase and cirrus clouds. The Ice Roughness Investigation System (IRIS) is a new laboratory setup designed to investigate the conditions under which roughness develops on single ice crystals, based on their size, morphology and growth conditions (relative humidity and temperature). Ice roughness is quantified through the analysis of speckle in 2-D light-scattering patterns. Characterization of the setup shows that a supersaturation of 20 % with respect to ice and a temperature at the sample position as low as-40 °C could be achieved within IRIS. Investigations of the influence of humidity show that higher supersaturations with respect to ice lead to enhanced roughness and irregularities of ice crystal surfaces. Moreover, relative humidity oscillations lead to gradual ratcheting-up of roughness and irregularities, as the crystals undergo repeated growth-sublimation cycles. This memory effect also appears to result in reduced growth rates in later cycles. Thus, growth history, as well as supersaturation and temperature, influences ice crystal growth and properties, and future atmospheric models may benefit from its inclusion in the cloud evolution process and allow more accurate representation of not just roughness but crystal size too, and possibly also electrification properties.Peer reviewe

A novel phase-aligned analysis on motion patterns of table tennis strokes

© 2016, Routledge. All rights reserved. A wide range of human motion represent repetitive patterns particularly in racket sports. Quantitative analysis of the continuous variables during the different phases of the motion cycle helps to investigate more deeply the specific movement of the racket or player. Table tennis biomechanics research to date lacks the necessary detail of phase decomposition and phase-based quantitative analysis. Therefore, this study proposes a novel velocity-based piecewise alignment method to identify the different phases of a table tennis forehand stroke. A controlled experiment was conducted on a number of players of two differing ability levels (experts vs. novices) to implement this novel methodology. Detailed results are shown for the quantitative analysis on multiple strokes of the two groups of participants. Significant differences were found in both the displacement and velocity of the racket movement in the backswing, forward swing and follow-through phases. For example, it is clear that experts’ strokes show higher racket resultant velocity than novices during both the forward swing and follow-through phases by up to a factor of two. Furthermore, the phase-based approach to analysing racket motions leads to interrogation over a greater duration than the traditional time-based method which is generally only concerned with impact ±0.25s

Drop formation due to turbulent primary breakup at the free surface of plane liquid wall jets

An experimental study of turbulent primary breakup at the free surface of plane liquid wall jets along smooth walls in still air at normal temperature and pressure is described. The study seeks a better understanding of spray formation processes in marine environments, such as in bow sheets. The measurements involved initially nonturbulent annular liquid wall jets, to approximate plane liquid wall jets, with the growth of a turbulent boundary layer along the wall initiated by a trip wire. Pulsed shadowgraphy and holography were used to observe liquid surface properties as well as drop sizes and velocities after turbulent primary breakup. Test conditions included several liquids (water, glycerol mixtures and ethyl alcohol), liquid/gas density ratios of 680–980, wall jet Reynolds numbers of 17 000–840 000 and Weber numbers of 6 100–57 000, at conditions where direct effects of liquid viscosity were small. Measurements included the following: location of the onset of surface roughness, drop size and velocity distributions after breakup, flow properties at the onset of breakup, and mean drop sizes and velocities after breakup. In general, the measurements were correlated successfully based on phenomenological theories. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70361/2/PHFLE6-10-5-1147-1.pd

Analysis and representation of statistical performance of JPEG2000 encoded image over wireless channels

JPEG2000 is a new coming image standard. In this paper we analyze the performance of error resilience tools in JPEG2000, and present an analytical model to estimate the quality of JPEG2000 encoded image transmitted over wireless channels. The effectiveness of the analytical model is validated by simulation results. Furthermore, analytical model is utilized by the base station to design efficient unequal error protection schemes for JPEG2000 transmission. In the design, a utility function is defined to make a tradeoff between the image quality and the cost for transmitting the image over a wireless channel

Shoulder joint angle errors caused by marker offset

Crown Copyright © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license. The International Society of Biomechanics (ISB) has recommended a standardization of the definition of the joint coordinate system (JCS) and use of a sequential rotation to describe human shoulder joint rotation. Markers attached to the surface of the body may move during the process of motion data capture, resulting in an offset from their initial location. This leads to a change of the JCS and therefore affects the calculated shoulder joint angles. In this research study, we presented a simple marker offset model to quantify the shoulder joint errors for both static poses and dynamic activities. Specific conditions of different offsets and elbow flexion angles were studied. Results showed that the errors should not be neglected when the shoulder elevation angle was near -90° and 90°, or elbow flexion was very small. Attention should be paid to these errors for such activities especially walking and throwing

Possible test for CPT invariance with correlated neutral B decays

We study breakdown of $CPT$ symmetry which can occur in the decay process $B \bar B \to l^\pm X^\mp f$ with $f$ being a CP eigenstate. In this process, the standard model expectations for time ordered semi-leptonic and hadronic events, i.e. which of the two decays takes place first, can be altered in the case that there is a violation of the $CPT$ symmetry. To illustrate this possibility, we identify and study several time integrated observables. We find that an experiment with $10^{9}$ $B\bar B$ pairs, has the capability for improving the bound on $CPT$ violating parameter or perhaps observe $CPT$ violation.Comment: Revised version to be published in PR