Class Of Collisions Research Articles

Thermodynamic model for electron emission and negative- and positive-ion formation in keV molecular collisions

A statistical-type model is developed to describe the ion production and electron emission in collisions of (molecular) ions with atoms. The model is based on the Boltzmann population of the bound electronic energy levels of the quasi molecule formed in the collision and the discretized continuum. The discretization of the continuum is implemented by a free electron gas in a box model assuming an effective square potential of the quasi molecule. The temperature of the electron gas is calculated by taking into account a thermodynamically adiabatic process due to the change of the effective volume of the quasi molecule as the system evolves. The system may undergo a transition with a small probability from the discretized continuum to the states of the complementary continuum. It is assumed that these states are decoupled from the thermodynamic time development. The decoupled states overwhelmingly determine the yield of the asymptotically observed fragment ions. The main motivation of this work is to describe the recently observed $H^-$ ion production in $OH^+ + Ar$ collisions. The obtained differential cross sections for $H^-$ formation, cation production and electron emission are close to the experimental ones. Calculations for the atomic systems $O^+ + Ar$ and $H^+ + Ar$ are also in reasonable agreement with the experiments indicating that the model can be applied to a wide class of collisions.

Traffic model by braking capability and response time

We propose a microscopic traffic model where the update velocity is determined by the deceleration capacity and response time. It is found that there is a class of collisions that cannot be distinguished by simply comparing the stop positions. The model generates the safe, comfortable, and efficient traffic flow in numerical simulations with a reasonable values of the parameters, and this is analytically supported. Our approach provides a new perspective in modeling traffic-flow safety and worrying situations like lane changing.

Human and organisational factors in maritime accidents: Analysis of collisions at sea using the HFACS

Over the last decade, the shipping industry has implemented a number of measures aimed at improving its safety level (such as new regulations or new forms of team training). Despite this evolution, shipping accidents, and particularly collisions, remain a major concern. This paper presents a modified version of the Human Factors Analysis and Classification System, which has been adapted to the maritime context and used to analyse human and organisational factors in collisions reported by the Marine Accident and Investigation Branch (UK) and the Transportation Safety Board (Canada).The analysis shows that most collisions are due to decision errors. At the precondition level, it highlights the importance of the following factors: poor visibility and misuse of instruments (environmental factors), loss of situation awareness or deficit of attention (conditions of operators), deficits in inter-ship communications or Bridge Resource Management (personnel factors). At the leadership level, the analysis reveals the frequent planning of inappropriate operations and non-compliance with the Safety Management System (SMS). The Multiple Accident Analysis provides an important finding concerning three classes of accidents. Inter-ship communications problems and Bridge Resource Management deficiencies are closely linked to collisions occurring in restricted waters and involving pilot-carrying vessels. Another class of collisions is associated with situations of poor visibility, in open sea, and shows deficiencies at every level of the socio-technical system (technical environment, condition of operators, leadership level, and organisational level). The third class is characterised by non-compliance with the SMS.This study shows the importance of Bridge Resource Management for situations of navigation with a pilot on board in restricted waters. It also points out the necessity to investigate, for situations of navigation in open sea, the masters’ decisions in critical conditions as well as the causes of non-compliance with SMS.