7,415 research outputs found
Non-strategic nuclear weapons: the next step in multilateral arms control
This paper by Crispin Rovere and Kalman A Robertson addresses the many barriers to including tactical nuclear weapons in disarmament talks. It considers the difficulty of bringing other emerging powers such as China into the nuclear arms control equation.
The study proposes a new arms control treaty that would ban outright the development and possession of a special kind of tactical nuclear weapon called \u27low-yield nuclear weapons\u27 that the authors argue carries an increasingly grave risk of starting a nuclear war.
The paper says that Australia should take the lead in promoting a new treaty banning low-yield nuclear weapons.
A longer discussion paper, which includes a more thorough exploration of the technical, strategic and legal issues, as well as many references for further reading is available below
Random sequential adsorption and diffusion of dimers and k-mers on a square lattice
We have performed extensive simulations of random sequential adsorption and
diffusion of -mers, up to in two dimensions with particular attention
to the case . We focus on the behavior of the coverage and of vacancy
dynamics as a function of time. We observe that for a complete coverage
of the lattice is never reached, because of the existence of frozen
configurations that prevent isolated vacancies in the lattice to join. From
this result we argue that complete coverage is never attained for any value of
. The long time behavior of the coverage is not mean field and nonanalytic,
with as leading term. Long time coverage regimes are independent of
the initial conditions while strongly depend on the diffusion probability and
deposition rate and, in particular, different values of these parameters lead
to different final values of the coverage. The geometrical complexity of these
systems is also highlighted through an investigation of the vacancy population
dynamics.Comment: 9 pages, 9 figures, to be published in the Journal of Chemical
Physic
A molecular dynamics simulation of water confined in a cylindrical SiO2 pore
A molecular dynamics simulation of water confined in a silica pore is
performed in order to compare it with recent experimental results on water
confined in porous Vycor glass at room temperature. A cylindrical pore of 40 A
is created inside a vitreous SiO2 cell, obtained by computer simulation. The
resulting cavity offers to water a rough hydrophilic surface and its geometry
and size are similar to those of a typical pore in porous Vycor glass. The
site-site distribution functions of water inside the pore are evaluated and
compared with bulk water results. We find that the modifications of the
site-site distribution functions, induced by confinement, are in qualitative
agreement with the recent neutron diffraction experiment, confirming that the
disturbance to the microscopic structure of water mainly concerns orientational
arrangement of neighbouring molecules. A layer analysis of MD results indicates
that, while the geometrical constraint gives an almost constant density profile
up to the layers closest to the interface, with an uniform average number of
hydrogen bonds (HB), the hydrophilic interaction produces the wetting of the
pore surface at the expenses of the adjacent water layers. Moreover the
orientational disorder togheter with a reduction of the average number of HB
persists in the layers close to the interface, while water molecules cluster in
the middle of the pore at a density and with a coordination similar to bulk
water.Comment: RevTex, 11 pages, 12 figures; to appear in June 15 issue of J. Chem.
Phy
Confined water in the low hydration regime
Molecular dynamics results on water confined in a silica pore in the low
hydration regime are presented. Strong layering effects are found due to the
hydrophilic character of the substrate. The local properties of water are
studied as function of both temperature and hydration level. The interaction of
the thin films of water with the silica atoms induces a strong distortion of
the hydrogen bond network. The residence time of the water molecules is
dependent on the distance from the surface. Its behavior shows a transition
from a brownian to a non-brownian regime approaching the substrate in agreement
with results found in studies of water at contact with globular proteins.Comment: 7 pages with 12 figures (RevTeX4). To be published on J. Chem. Phy
Modifications of the hydrogen bond network of liquid water in a cylindrical SiO_2 pore
We present results of molecular dynamics simulations of water confined in a
silica pore. A cylindrical cavity is created inside a vitreous silica cell with
geometry and size similar to the pores of real Vycor glass. The simulations are
performed at different hydration levels. At all hydration levels water adsorbs
strongly on the Vycor surface; a double layer structure is evident at higher
hydrations. At almost full hydration the modifications of the
confinement-induced site-site pair distribution functions are in qualitative
agreement with neutron diffraction experiment. A decrease in the number of
hydrogen bonds between water molecules is observed along the pore radius, due
to the tendency of the molecules close to the substrate to form hydrogen-bonds
with the hydrophilic pore surface. As a consequence we observe a substrate
induced distortion of the H-bond tetrahedral network of water molecules in the
regions close to the surface.Comment: Talk presented at "Physics of Liquids: Foundations, Highlights,
Challenge", Murau Sept. 1998. To appear in J. Mol. Li
A standardized database of Last Interglacial (MIS 5e) sea-level indicators in Southeast Asia
Marine Isotope Stage 5e (MIS 5e; the Last Interglacial, 125 ka) represents a process analog for a warmer world. Analysis of sea-level proxies formed in this period helps in constraining both regional and global drivers of sea-level change. In Southeast Asia, several studies have reported elevation and age information on MIS 5e sea-level proxies, such as fossil coral reef terraces or tidal notches, but a standardized database of such data was hitherto missing. In this paper, we produced such a sea-level database using the framework of the World Atlas of Last Interglacial Shorelines (WALIS; https://warmcoasts.eu/world-atlas.html). Overall, we screened and reviewed 14 studies on Last Interglacial sea-level indicators in Southeast Asia, from which we report 43 proxies (42 coral reef terraces and 1 tidal notch) that were correlated to 134 dated samples. Five data points date to MIS 5a (80 ka), six data points are MIS 5c (100 ka), and the rest are dated to MIS 5e. The database compiled in this study is available at 10.5281/zenodo.5040784 (Maxwell et al., 2021)
Layer Analysis of the Structure of Water Confined in Vycor Glass
A Molecular Dynamics simulation of the microscopic structure of water
confined in a silica pore is presented. A single cavity in the silica glass has
been modeled as to reproduce the main features of the pores of real Vycor
glass. A layer analysis of the site-site radial distribution functions evidence
the presence in the pore of two subsets of water molecules with different
microscopic structure. Molecules which reside in the inner layer, close to the
center of the pore, have the same structure as bulk water but at a temperature
of 30 K higher. On the contrary the structure of the water molecules in the
outer layer, close to the substrate, is strongly influenced by the
water-substrate hydrophilic interaction and sensible distortions of the H-bond
network and of the orientational correlations between neighboring molecules
show up. Lowering the hydration has little effect on the structure of water in
the outer layer. The consequences on experimental determinations of the
structural properties of water in confinement are discussed.Comment: 6 pages, 8 figures included in the text, one figure added, changes in
the tex
Assessing enigmatic boulder deposits in NE Aegean Sea: importance of historical sources as tool to support hydrodynamic equations
Due to their importance in the assessment of coastal hazards, several studies have focused on geomorphological and sedimentological field evidence of catastrophic wave impacts related to historical tsunami events. Among them, many authors used boulder fields as important indicators of past tsunamis, especially in the Mediterranean Sea. The aim of this study was to understand the mechanism of deposition of clusters of large boulders, consisting of beachrock slabs, which were found on the southern coasts of Lesvos Island (NE Aegean Sea). Methods to infer the origin of boulder deposits (tsunami vs. storm wave) are often based on hydrodynamic models even if different environmental complexities are difficult to be incorporated into numerical models. In this study, hydrodynamic equations did not provide unequivocal indication of the mechanism responsible for boulder deposition in the study area. Further analyses, ranging from geomorphologic to seismotectonic data, indicated a tsunami as the most likely cause of displacement of the boulders but still do not allow to totally exclude the extreme storm origin. Additional historical investigations (based on tsunami catalogues, historical photos and aged inhabitants interviews) indicated that the boulders are likely to have been deposited by the tsunami triggered by the 6.7 <i>M</i><sub>s</sub> Chios-Karaburum earthquake of 1949 or, alternatively, by minor effects of the destructive tsunami produced by 1956's Amorgos Island earthquake. Results of this study point out that, at Mediterranean scale, to flank numerical models with the huge amount of the available historical data become a crucial tool in terms of prevention policies related to catastrophic coastal events
Spinodal of supercooled polarizable water
We develop a series of molecular dynamics computer simulations of liquid
water, performed with a polarizable potential model, to calculate the spinodal
line and the curve of maximum density inside the metastable supercooled region.
After analysing the structural properties,the liquid spinodal line is followed
down to T=210 K. A monotonic decrease is found in the explored region. The
curve of maximum density bends on approaching the spinodal line. These results,
in agreement with similar studies on non polarizable models of water, are
consistent with the existence of a second critical point for water.Comment: 8 pages, 5 figures, 2 tables. To be published in Phys. Re
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