Search results for "Liquid water"

Behaviour of Interacting Protons: The Average-Mass Approach to its Study and its Possible Biological Relevance

1973

Among all other kinds of ions occurring in the solid, liquid and living states of matter, positive hydrogen ions (which we shall henceforth call protons for brevity) are singled out by their exceptionally small mass. This is the reason for their specific property of tunnelling through potential barriers, which in turn is responsible for such properties as hydrogen bonding. This is also responsible for the unique properties exhibited in many cases by (sub)systems of interacting protons. Examples are the intriguing properties of liquid water and ice [1]; the para-ferroelectric transition in hydrogen-bonded ferroelectrics [2]; the cooperative transitions in ammonium salts [3] and in hexamine h…

Monte Carlo calculation of dose rate distributions around 192Ir wires.

1997

Monte Carlo calculations of absolute dose rate in liquid water are presented in the form of away-along tables for 1 and 5 cm 192 Ir wires of 0.3 mm diameter. Simulated absolute dose rate values can be used as benchmark data to verify the calculation results of treatment planning systems or directly as input data for treatment planning. Best fit value of attenuation coefficient suitable for use in Sievert-integrals-type calculations has been derived based on Monte Carlo calculation results. For the treatment planning systems that are based on TG43 formalism we have also calculated the required dosimetry parameters.

Energy loss measurement of protons in liquid water

2011

The proton stopping power of liquid water was, for the first time, measured in the energy range 4.7-15.2 MeV. The proton energies were determined by the time-of-flight transmission technique with the microchannel plate detectors, which were especially developed for timing applications. The results are compared to the literature values (from ICRU Report 49 (1993) and Janni's tabulation (1982 At. Data Nucl. Data Tables 27 147-339)) which are based on Bethe's formula and an agreement is found within the experimental uncertainty of 4.6%. Thus, earlier reported discrepancy between the experimental and literature stopping power values at lower energies was not observed at the energies considered …

Explicit cloud-top entrainment parameterization in the global climate model ECHAM5-HAM

2011

New developments in the turbulence parameterization in the general circulation model ECHAM5-HAM are presented. They consist mainly of an explicit entrainment closure at the top of stratocumulus-capped boundary layers and the addition of an explicit contribution of the radiative divergence in the buoyancy production term. The impact of the new implementations on a single column model study and on the global scale is presented here. The parameterization has a "smoothing" effect: the abnormally high values of turbulence kinetic energy are reduced, both in the single column and in the Californian stratocumulus region. A sensitivity study with prescribed droplet concentration shows a reduction i…

Cloud and Fog Effects and Their Parameterisation in Regional Air Quality Models

1997

For the special purpose of cloud chemistry a tool ASOCC was developed which is able to generate a differential equation system from a given set of chemical kinetics equations. Sensitivity and structure analysis have been performed to evaluate the great number of investigated reactions in the liquid phase and to derive a condensed mechanism for use in regional chemistry-transport models.

The Search Starts

2010

The previous chapter has shown us that life on Earth arose surprisingly fast and easy, as soon as the conditions were right for liquid water to be sustained on the surface. We saw that there is evidence of the presence of this valuable substance in at least two other bodies in the Solar System, and these are encouraging indications that life in the Solar System might not be limited to Earth. Also, we saw that planetary systems are not rarities of nature but seem to abound across the universe, and that life is much more resistant than was once believed, which extends the limits of what can be considered a habitable world. All these facts, despite our own ignorance about many things, make num…

Effects of organic aerosol constituents on extinction and absorption coefficients and liquid water contents of fogs and clouds

1978

We have speculated on the influence of organic material on extinction and absorption coefficients and liquid water content of fogs and of clouds immediately after their condensational stage. It results therefore, that the reduction of the speed of growth from fog to cloud droplets due to the presence of organic films largely reduces the properties mentioned. Compared to that their increase coming from the surface tension reduction due to organic material being dissolved or building up films is expected to be less effective.

2014

Abstract. This study uses the EMAC atmospheric chemistry-climate model to simulate cloud properties and estimate cloud radiative effects induced by aerosols. We have tested two prognostic cloud droplet nucleation parameterizations, i.e., the standard STN (osmotic coefficient model) and hybrid (HYB, replacing the osmotic coefficient by the κ hygroscopicity parameter) schemes to calculate aerosol hygroscopicity and critical supersaturation, and consider aerosol–cloud feedbacks with a focus on warm clouds. Both prognostic schemes (STN and HYB) account for aerosol number, size and composition effects on droplet nucleation, and are tested in combination with two different cloud cover parameteriz…

Ultrathin Tropical Tropopause Clouds (UTTCs): II. Stabilization mechanisms

2003

Abstract. Mechanisms by which subvisible cirrus clouds (SVCs) might contribute to dehydration close to the tropical tropopause are not well understood. Recently Ultrathin Tropical Tropopause Clouds (UTTCs) with optical depths around 10-4 have been detected in the western Indian ocean. These clouds cover thousands of square kilometers as 200-300 m thick distinct and homogeneous layer just below the tropical tropopause. In their condensed phase UTTCs contain only 1-5% of the total water, and essentially no nitric acid. A new cloud stabilization mechanism is required to explain this small fraction of the condensed water content in the clouds and their small vertical thickness. This work sugges…

Cationic and Anionic Impact on the Electronic Structure of Liquid Water

2017

Hydration shells around ions are crucial for many fundamental biological and chemical processes. Their local physicochemical properties are quite different from those of bulk water and hard to probe experimentally. We address this problem by combining soft X-ray spectroscopy using a liquid jet and molecular dynamics (MD) simulations together with ab initio electronic structure calculations to elucidate the water–ion interaction in a MgCl2 solution at the molecular level. Our results reveal that salt ions mainly affect the electronic properties of water molecules in close vicinity and that the oxygen K-edge X-ray emission spectrum of water molecules in the first solvation shell differs signi…